[QUIZ] Fuzzy Time (#99)

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···

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

by Gavin Kistner

  The Background
  ---------------------------------------------------------------------

Last night I was having trouble falling asleep, and was staring at my digital
alarm clock (as I do so often under that circumstance). Something on the bedside
table was occluding the minutes digit, however, so all I could tell is that it
was "10 4". (Oddly, my alarm clock has no ":" between the hours and minutes.)

"How nice!" I thought. "An imposed vagueness to keep me from obsessing on
exactly what time it is! Should I really be worried about the exact time?
Shouldn't I be more relaxed? Shouldn't a 10-minute precision in life be enough
to keep me roughly on time, without obsessing on exacting promptitude?"

I realized that if I kept staring at the clock (as I did), and I were to observe
it changing from "10 4" to "10 5", that I would, at that moment, know exactly
what time it is.

"Bah" I thought, "so much for that idea."

And then I thought some more. I thought of bad ideas: analog watches where the
hand erratically swings forward and backward, digital clocks that showed random
times near the correct time. And then I dreamed of the watch I wanted to own...

  The Challenge
  ---------------------------------------------------------------------

Requirement #1: Write a Ruby program that shows the current time, but only the
'tens' part of the minutes. For example, if the time is 10:37, then the program
might output "10:3~"

Requirement #2: The time shown by the clock must randomly vary +/- 5 minutes
from reality. For example, if the time is actually 10:37, the program might
output "10:3~" or "10:4~" (but not "10:2~" or "10:5~").

Requirement #3: The time on the clock should continuously increase. If the time
shows "10:4~" it must continue to show "10:4~" until it shows "10:5~". (It can't
show "10:4~", then "10:3~" for a bit and then come back to "10:4~".)

Putting the three requirements together, the left column below shows the actual
time and the next three columns show the possible outputs from three different
runs of the same program:

  10:35 10:3~ 10:4~ 10:3~
  10:36 10:3~ 10:4~ 10:3~
  10:37 10:3~ 10:4~ 10:3~
  10:38 10:3~ 10:4~ 10:3~
  10:39 10:4~ 10:4~ 10:3~
  10:40 10:4~ 10:4~ 10:3~
  10:41 10:4~ 10:4~ 10:3~
  10:42 10:4~ 10:4~ 10:3~
  10:43 10:4~ 10:4~ 10:3~
  10:44 10:4~ 10:4~ 10:3~
  10:45 10:4~ 10:4~ 10:4~
  10:46 10:4~ 10:4~ 10:5~
  10:47 10:4~ 10:4~ 10:5~
  10:48 10:4~ 10:4~ 10:5~
  10:49 10:4~ 10:4~ 10:5~
  10:50 10:4~ 10:4~ 10:5~
  10:51 10:4~ 10:4~ 10:5~
  10:52 10:5~ 10:4~ 10:5~
  10:53 10:5~ 10:4~ 10:5~
  10:54 10:5~ 10:4~ 10:5~
  10:55 10:5~ 10:5~ 10:5~
  10:56 10:5~ 10:5~ 11:0~
  10:57 10:5~ 10:5~ 11:0~
  10:58 10:5~ 10:5~ 11:0~
  10:59 10:5~ 10:5~ 11:0~
  11:00 10:5~ 10:5~ 11:0~
  11:01 10:5~ 10:5~ 11:0~

  Testing your Output
  ---------------------------------------------------------------------

You should supply a FuzzyTime class that supports the following:

  ft = FuzzyTime.new # Start at the current time
  ft = FuzzyTime.new(Time.at(1161104503)) # Start at a specific time
  
  p ft.to_s # to_s format
  #=> "10:5~"
  
  p ft.actual, ft.actual.class # Reports real time as Time
  #=> Tue Oct 17 11:01:36 -0600 2006
  #=> Time
  
  ft.advance( 60 * 10 ) # Manually advance time
  puts ft # by a specified number of
  #=> 11:0~ # seconds.
  
  sleep( 60 * 10 )
  
  ft.update # Automatically update the time based on the
  puts ft # time that has passed since the last call
  #=> 11:1~ # to #initialize, #advance or #update

Your class and output will be tested with code like the following:

  def test_output
    # Initialize with a well-known time
    ft = FuzzyTime.new( Time.at( ... ) )
    
    60.times do
      @legal = ... # Find the array of legal output strings
      @output = ft.to_s
      
      assert_block "#@output not one of #@legal.inspect" do
        @legal.include?( @output )
      end
      
      sleep( rand( 30 ) )
      ft.update
    end
    
    60.times do
      @legal = ... # Find the array of legal output strings
      @output = ft.to_s
      
      assert_block "#@output not one of #@legal.inspect" do
        @legal.include?( @output )
      end
      
      ft.advance( rand( 30 ) )
    end
  end

  Extra Credit
  ---------------------------------------------------------------------

  * Provide a self-running application that shows the time somehow.
  (ASCII in the terminal, some GUI window, etc.)
  
  * Allow your class to be customized to display 12- or 24-hour time.
  
  * Allow your class to be customized to change how close to reality
  it must display. (+/- 3 minutes, +/- 12 minutes, etc.)
  
  * Allow your class to be customized to change how roughly it displays
  the time (e.g. 1 minute, 10 minute, 1 hour intervals).
  
  * Ensure that the transition from one digit to the next occurs
  randomly across the range of -5 to +5. (So, while the digit might
  change 5 minutes before or 5 minutes after the real transition, on
  average the change should occur around the transition itself.)
  You might need to assume that your update/advance method will be
  called with a certain regularity (e.g. once per second, once every
  7 seconds, once every 30 seconds, etc.)
  
  * Come up with your own technique of displaying time that
  (a) is always 'close' to right, but (b) never allows a
  watchful person to ever know exactly what time it is.

  Things to Keep in Mind
  ---------------------------------------------------------------------

  * You need to be able to handle the transition across hour/day
  boundaries. (10:5~ might change to 11:0~ when the real time is still
  10:58, or might continue to display 10:5~ when the real time is
  11:04. On a 24-hour click, you also need to be able to wrap from
  23:5~ to 00:0~)
  
  * For testing purposes of the real-time #update advancing, you might
  find it easier to work with minutes and seconds instead of hours and
  minutes.
  
  * Requirement #3 is, well, a requirement. Repeated #update/#to_s
  calls to a FuzzyTime instance should never show an earlier time
  (unless 24 hours occurred between #update calls ;).

2

it seems like #2 and #3 contradict one another. imagine it's 10:45 and,
through randomness, you choose to vary the clock by +5, therefore displaying
10:5~, you will not be able to change the output again until 10:55, and then
only because the upper bould will have rolled over into the next hour. here it
is in table form

   ----- ------ ----- ---------
   lower actual upper selection
   ----- ------ ----- ---------
   10:40 10:45 10:50 10:50/5~
   10:41 10:46 10:51 10:51/5~
   10:42 10:47 10:52 10:52/5~
   10:43 10:48 10:53 10:53/5~
   10:44 10:49 10:54 10:54/5~
   10:45 10:50 10:55 10:55/5~
   10:46 10:51 10:56 10:56/5~
   10:47 10:52 10:57 10:57/5~
   10:48 10:53 10:58 10:58/5~
   10:49 10:54 10:59 10:59/5~
   10:50 10:55 11:00 11:00/0~

an initial high selection eats into subsequent ranges - in otherwords a
selection of t+ means that #2 will not by able to hold: the variance will be
required to b smaller for the next choice: a high selection eats the variance
range of the next choice...

it's possibly even worse when we not near the top of an hour and start of with
maximum variance:

   ----- ------ ----- ---------
   lower actual upper selection
   ----- ------ ----- ---------
   10:20 10:25 10:30 10:30/3~
   10:21 10:26 10:31 10:31/3~
   10:22 10:27 10:32 10:32/3~
   10:23 10:28 10:33 10:33/3~
   10:24 10:29 10:34 10:34/3~
   10:25 10:30 10:35 10:35/3~
   10:26 10:31 10:36 10:36/3~
   10:27 10:32 10:37 10:37/3~
   10:28 10:33 10:38 10:38/3~
   10:29 10:34 10:39 10:39/3~
   10:30 10:35 10:40 10:30/3~
   10:31 10:36 10:41 10:31/3~
   10:32 10:37 10:42 10:32/3~
   10:33 10:38 10:43 10:33/3~
   10:34 10:39 10:44 10:34/3~
   10:35 10:40 10:45 10:35/3~
   10:36 10:41 10:46 10:36/3~
   10:37 10:42 10:47 10:37/3~
   10:38 10:43 10:48 10:38/3~
   10:39 10:44 10:49 10:39/3~
   10:40 10:45 10:50 10:50/5~

so the combined effect means that it's acceptable to display the same time~
for twenty straight minutes - is that really the a desired potential effect?

-a

···

On Fri, 27 Oct 2006, Ruby Quiz wrote:

  The Challenge
  ---------------------------------------------------------------------

Requirement #1: Write a Ruby program that shows the current time, but only the
'tens' part of the minutes. For example, if the time is 10:37, then the program
might output "10:3~"

Requirement #2: The time shown by the clock must randomly vary +/- 5 minutes
from reality. For example, if the time is actually 10:37, the program might
output "10:3~" or "10:4~" (but not "10:2~" or "10:5~").

Requirement #3: The time on the clock should continuously increase. If the time
shows "10:4~" it must continue to show "10:4~" until it shows "10:5~". (It can't
show "10:4~", then "10:3~" for a bit and then come back to "10:4~".)

--
my religion is very simple. my religion is kindness. -- the dalai lama

3

#!/usr/bin/env ruby

···

################################################################################
# quiz99.rb: Implementation of RubyQuiz #99 - Fuzzy Time
#
# Lou Scoras <louis.j.scoras@gmail.com>
# Sunday, October 29th, around 11 o-clock (*smirks*).
#
# I decided to approximate time to the quarter hour. When people on the street
# bother you for the time, that's probably what they are expecting. It's been
# my experience that they give you nasty looks when you make them do any
# amount of trivial math =)
#
# This one was a lot of fun. Thanks again to James and Gavin for another great
# quiz.
#
################################################################################

class Time

  # A string representation for times on the quarter hour

  def to_quarter_s
    case min
      when 0
        "#{hour_12} o-clock"
      when 15
        "quarter past #{hour_12}"
      when 30
        "half past #{hour_12}"
      when 45
        n = self + 3600
        "quarter 'till #{n.hour_12}"
    end
  end

  # Let the Time library to the hard work for getting 12 time.

  def hour_12
    (strftime "%I").sub(/\A0/,'')
  end
end

class FuzzyTime

  # Quarter hours fall every 900 seconds

  TimeScale = 60 * 15

  def initialize(time = Time.now)
    @real = @time = time
    @emitted = nil
  end

  # Use a simple linear scaling to even out the intervals. This seems to work
  # out okay after a little testing, but it could probably be improved quite a
  # bit.
  #
  # One variable that effects this is the sampling rate. We're approximating to
  # the nearest quarter hour; however, if you call to_s say once a second, you
  # have a greater chance of bumping up to the next interval than if you
  # increase the time between calls to one minute.

  def to_s
    pick = rand(TimeScale)
    threshold = TimeScale - @time.to_i % TimeScale - 1
    p [pick, threshold, last_valid, next_valid] if $DEBUG

    @emitted = if (!@emitted.nil? && @emitted > last_valid) \
               >> pick >= threshold
      next_valid
    else
      last_valid
    end

    @emitted.to_quarter_s
  end

  def inspect
    t_obj = if @emitted.nil?
      self.class.new(@time).next_valid
    else
      @emitted
    end
    %!FuzzyTime["#{t_obj.to_quarter_s}"]!
  end

  def actual
    @time
  end

  def last_valid
    Time.at(@time.to_i / TimeScale * TimeScale)
  end

  def next_valid
    last_valid + TimeScale
  end

  def advance(offset)
    @real = Time.now
    @time += offset
    offset
  end

  def update
    now = Time.now
    delta = now - @real
    @time += delta
    @real = now
  end

end

# Err, I forgot what the incantation is on windows. I think it is 'cls', but
# I'll leave it as an exercise to the reader. *winks*

ClearString = `clear`
def clear
  print ClearString
end

def get_sample_rate
  default = 60
  return default unless ARGV[0]
  begin
    return ARGV[0].to_i
  rescue
    return default
  end
end

if caller.empty?
  ft = FuzzyTime.new

  while true do
    clear
    puts ft
    sleep get_sample_rate
    ft.update
  end
end

4

Thanks for this week's interesting problem. My solution is below and
I look forward to any feedback and seeing other techniques used.

There are two files pasted below; the second is the unit test, which
takes about 5-10 minutes to run to completion. My first unit test
ever in any language :slight_smile:

This is also my first greeting to the Ruby community... Hello!

Cheers,
Marcel

#!/usr/bin/env ruby

···

#
# Marcel Ward <wardies ^a-t^ gmaildotcom>
# Sunday, 29 October 2006
# Solution for Ruby Quiz number 99
#
################################################
# fuzzy_time.rb

class FuzzyTime
  attr_reader :actual, :timed_observation_period

  # If the time passed is nil, then keep track of the time now.
  def initialize(tm=nil, range_secs=600, disp_accuracy_secs=range_secs,
                  fmt="%H:%M", obs_period=nil)
    @actual = @last_update = @next_diff = tm || Time.now
    @realtime = tm.nil?
    @maxrange = range_secs
    @display_accuracy = @best_accuracy = disp_accuracy_secs
    @tformat = fmt
    @last_observed = @max_disptime = Time.at(0)
    @timed_observation_period = obs_period
  end

  def to_s
    @last_update = Time.now
    @actual = @last_update if @realtime

    check_observation_period unless @timed_observation_period.nil?

  # We only calculate a new offset each time the last offset times out.
    if @next_diff <= @actual
      # Calculate a new time offset
      @diff = rand(@maxrange) - @maxrange/2
      # Decide when to calculate the next time offset
      @next_diff = @actual + rand(@maxrange)
    end
    @last_observed = @actual

    # Don't display a time less than the time already displayed
    @max_disptime = [@max_disptime, @actual + @diff].max

    # Take care to preserve any specific locale (time zone / dst) information
    # stored in @actual - for example, we cannot use Time::at(Time::to_i).
    disptime = @max_disptime.strftime(@tformat)

    # Lop off characters from the right of the display string until the
    # remaining string matches one of the extreme values; then fuzz out the
    # rightmost digits
    (0..disptime.size).to_a.reverse.each do
      >w>
      [@display_accuracy.div(2), - @display_accuracy.div(2)].map{
        >offs>
        (@max_disptime + offs).strftime(@tformat)
      }.each do
        >testtime>
        return disptime[0,w] + disptime[w..-1].tr("0123456789", "~") if \
          disptime[0,w] == testtime[0,w]
      end
    end
  end

  def advance(secs)
    if @realtime
      @actual = Time.now + secs
      # Once a real-time FuzzyTime is advanced, it can never again be
      # real-time.
      @realtime = false
    else
      @actual += secs
    end
    @last_update = Time.now
  end

  def update
    diff = Time.now - @last_update
    @actual += diff
    @last_update += diff
    # By calling update, you are effectively saying "set a fixed time"
    # so we must disable the real-time flag.
    @realtime = false
  end

  def accuracy
    "+/- #{@maxrange/2}s"
  end

  def dump
    "actual: #{@actual.strftime("%Y-%m-%d %H:%M:%S")}, " \
    "diff: #{@diff}, " \
    "next_diff: #{@next_diff.strftime("%Y-%m-%d %H:%M:%S")}, " \
    "accuracy: #{@display_accuracy}"
  end

private
  def check_observation_period
    # Is the clock being displayed too often?

    # Although this method seems to work, it may be a bit simplistic.
    # Proper statistical / mathematical analysis and a proper understanding
    # of the human ability to count seconds may be necessary to determine
    # whether this still gives away too much info for the average observer.

    patience = @actual - @last_observed

    if patience < @timed_observation_period / 2
      # Worsen display accuracy according to how impatient the observer is.
      @display_accuracy += (2 * @best_accuracy *
                            (@timed_observation_period - patience)) /
                            @timed_observation_period
    elsif patience < @timed_observation_period
      # Immediately punish impatience by enforcing a minumum accuracy
      # twice as bad as the best possible.
      # Don't give too much away but allow the accuracy to get slowly better
      # if the observer is a bit more patient and waits over half the
      # observation period
      @display_accuracy = [
          2 * @best_accuracy,
          @display_accuracy - ((@best_accuracy * patience) /
                                @timed_observation_period)
        ].max
    else
      # The observer has waited long enough.
      # Reset to the best possible accuracy.
      @display_accuracy = @best_accuracy
    end
  end
end

def wardies_clock
  # Get us a real-time clock by initializing Time with first parameter==nil
  # Make the seconds harder to guess by expanding the range to +/- 15s whilst
  # keeping the default display accuracy to +/- 5 secs. The user will have
  # to wait 30s between observations to see the clock with best accuracy.
  ft = FuzzyTime.new(nil, 30, 10, "%H:%M:%S", 30)

  # This simpler instantiation does not check the observation period and
  # shows "HH:M~". (This is the default when no parameters are provided)
  #ft = FuzzyTime.new(nil, 600, 600, "%H:%M")

  puts "** Wardies Clock\n"
  puts "**\n** Observing more often than every " \
    "#{ft.timed_observation_period} seconds reduces accuracy" \
    unless ft.timed_observation_period.nil?
  puts "**\n\n"

  loop do
    puts "\n\nTime Now: #{ft.to_s} (#{ft.accuracy})\n\n" \
      "-- Press Enter to observe the clock again or " \
      "q then Enter to quit --\n\n"

    # Flush the output text so that we can scan for character input.
    STDOUT.flush

    break if STDIN.getc == ?q
  end
end

def clocks_go_back_in_uk
  # Clocks go back in the UK on Sun Oct 29. (+0100 => +0000)
  # Start at Sun Oct 29 01:58:38 +0100 2006
  ft = FuzzyTime.new(Time.at(Time.at(1162083518)))

  # In the UK locale, we see time advancing as follows:
  # 01:5~
  # 01:0~ (clocks gone back one hour)
  # 01:0~
  # ...
  # 01:0~
  # 01:1~

  60.times do
    puts ft.to_s
    ft.advance(rand(30))
  end
end

def full_date_example
  # Accuracy can be set very high to fuzz out hours, days, etc.
  # E.g. accuracy of 2419200 (28 days) fuzzes out the day of the month
  # Note the fuzz factoring does not work so well with hours and
  # non-30-day months because these are not divisble exactly by 10.

  tm = FuzzyTime.new(nil, 2419200, 2419200, "%Y-%m-%d %H:%M:%S")
  300.times do
    puts "#{tm.to_s} (#{tm.dump})"
    # advance by about 23 days
    tm.advance(rand(2000000))
    #sleep 0.2
  end
end

# Note, all the examples given in the quiz are for time zone -0600.
# If you are in a different timezone, you should see other values.
def quiz_example
  ft = FuzzyTime.new # Start at the current time
  ft = FuzzyTime.new(Time.at(1161104503)) # Start at a specific time

  p ft.to_s # to_s format

  p ft.actual, ft.actual.class # Reports real time as Time
  #=> Tue Oct 17 11:01:36 -0600 2006
  #=> Time

  ft.advance( 60 * 10 ) # Manually advance time
  puts ft # by a specified number of
  #=> 11:0~ # seconds.

  sleep( 60 * 10 )

  ft.update # Automatically update the time based on the
  puts ft # time that has passed since the last call
  #=> 11:1~ # to #initialize, #advance or #update
end

if __FILE__ == $0
  wardies_clock
  #clocks_go_back_in_uk
  #full_date_example
  #quiz_example
end

################################################
# fuzzy_time_test.rb

require 'test/unit'
require 'fuzzy_time'

class FuzzyTime_Test < Test::Unit::TestCase
  #def setup
  #end

  #def teardown
  #end

  def test_advance

    # Initialize with a known UTC time (Tue Jun 10 03:14:52 UTC 1975)
    ft = FuzzyTime.new(Time.at(171602092).getgm, 60, 60, "%H:%M:%S")

    # Add 6 hours 45 minutes 30 secs to give us
    # (Tue Jun 10 09:59:22 UTC 1975)
    ft.advance(3600*6 + 60*45 + 30)
    @last_output = ""

    60.times do
      # Initial displayed time sourced from between 09:58:52 and 09:59:52
      # Time will be advanced by between 0 and 600 seconds.
      # So final displayed time source ranges from 10:08:52 to 10:09:52

      # The array of legal output strings:
      @legal = ["09:58:~~", "09:59:~~", "10:00:~~", "10:01:~~",
        "10:02:~~", "10:03:~~", "10:04:~~", "10:05:~~",
        "10:06:~~", "10:07:~~", "10:08:~~", "10:09:~~"]

      @output = ft.to_s

      assert_block "#@output not one of #{@legal.inspect}" do
        @legal.include?( @output )
      end

      assert_block "#@output must be greater than or equal to " \
        "last value, #@last_output" \
      do
        @output >= @last_output
      end
      @last_output = @output

      ft.advance( rand( 11 ) )
    end
  end

  def test_advance_rollover
    # Initialize with a known UTC time (Fri Dec 31 23:58:25 UTC 1999)
    # Test rollover at midnight
    # Note, we have an accuracy of +/- 5 secs now and enabled the
    # observations timer
    ft = FuzzyTime.new(Time.at(946684705).getgm, 10, 10, "%H:%M:%S", 10)

    30.times do
      # Initial displayed time sourced from between 23:58:20 and 23:58:30
      # Time will be advanced by between 0 and 150 seconds.
      # So final displayed time source ranges from 00:00:50 to 00:01:00

      # Note, if we watch too often over a short period of time,
      # our displayed accuracy will decrease. Then we will lose
      # the 10's digit of the seconds and occasionally the 1's minute.

      # The array of legal output strings:
      @legal = ["23:58:1~", "23:58:2~", "23:58:3~",
        "23:58:4~", "23:58:5~", "23:58:6~",
        "23:58:~~", "23:59:~~", "23:5~:~~",
        "23:59:0~", "23:59:1~", "23:59:2~",
        "23:59:3~", "23:59:4~", "23:59:5~",
        "00:00:0~", "00:00:1~", "00:00:2~",
        "00:00:3~", "00:00:4~", "00:00:5~", "00:00:~~",
        "00:01:0~", "00:01:~~", "00:0~:~~"]

      @output = ft.to_s

      assert_block "#@output not one of #{@legal.inspect}" do
        @legal.include?( @output )
      end

      # We cannot easily check that the current output is greater or equal to
      # the last because with timed observations, a valid output sequence is:
      # 23:59:0~
      # 23:59:~~ (looking too often, accuracy has been reduced)
      # 23:59:0~ (waited long enough before observing for accuracy to return)

      ft.advance( rand(6) )
    end
  end

  def test_update
    # NOTE - this test takes 5-10 minutes to complete

    # Initialize with a known UTC time (Tue Jun 10 03:14:52 UTC 1975)
    ft = FuzzyTime.new(Time.at(171602092).getgm, 60, 60, "%H:%M:%S")
    @last_output = ""

    60.times do
      # Initial displayed time sourced from between 03:14:22 and 03:15:22
      # Duration of loop will be between 0 and ~600 seconds.
      # So final displayed time source ranges from 03:14:22 to 03:25:22

      # The array of legal output strings:
      @legal = ["03:14:~~", "03:15:~~", "03:16:~~", "03:17:~~",
        "03:18:~~", "03:19:~~", "03:20:~~", "03:21:~~",
        "03:22:~~", "03:23:~~", "03:24:~~", "03:25:~~"]

      @output = ft.to_s

      assert_block "#@output not one of #{@legal.inspect}" do
        @legal.include?( @output )
      end

      assert_block "#@output must be greater than or equal to " \
        "last value, #@last_output" \
      do
        @output >= @last_output
      end
      @last_output = @output

      sleep( rand( 11 ) ) # wait between 0..10 secs
      ft.update
    end
  end
end

5

Here's my effort. I didn't get around to testing it, but the concept seems sound. I decided to interpret the goal a little more conservatively and instead of just making sure the displayed time never goes forward, I decided to make sure the offset never goes backwards. To do this, I made the max delta from the current offset no more than the amount of time that passed since the last offset update:

class FuzzyTime
   MAX_OFFSET = 5*60

   def initialize(*args)
     now = Time.new
     @internal_time = args[0] || now
     @time_offset = now - @internal_time
     @fuzzy_secs = 0
     @last_calc = Time.new
   end

   def actual
     @internal_time
   end

   def update
     @internal_time = Time.new + @time_offset
   end

   def advance(amount)
     @time_offset += amount.to_i
   end

   def calc_offset
     # Choose a new offset that's between +/- 5 mins. If it has been
     # less than 5 mins since the last offset calc, choose that time as
     # a max delta (this makes sure time is always going forward)

     time_from_last_calc = (Time.new - @last_calc).to_i

     if time_from_last_calc > 0
       begin
         max_delta = [MAX_OFFSET, time_from_last_calc].min

         delta = rand((2*max_delta) + 1) - max_delta
       end until (delta + @fuzzy_secs).abs < MAX_OFFSET
       @fuzzy_secs += delta

       puts "Fuzzy secs now: #{@fuzzy_secs}"

       @last_calc = Time.new
     end
     @fuzzy_secs
   end

   def get_time
     fuzzy_hour = @internal_time.hour
     fuzzy_min = @internal_time.min
     fuzzy_sec = @internal_time.sec + calc_offset

     if fuzzy_sec > 60
       fuzzy_sec -= 60
       fuzzy_min += 1
     end

     if fuzzy_sec < 0
       fuzzy_sec += 60
       fuzzy_min -= 1
     end

     if fuzzy_min > 60
       fuzzy_min -= 60
       fuzzy_hour = (fuzzy_hour + 1) % 24
     end

     if fuzzy_min < 0
       fuzzy_min += 60
       fuzzy_hour = (fuzzy_hour + 23) % 24
     end

     [fuzzy_hour, fuzzy_min, fuzzy_sec]
   end

   def to_s
     fuzzy_hour, fuzzy_min, fuzzy_sec = get_time
     "#{fuzzy_hour}:#{fuzzy_min / 10}~"
     # "#{fuzzy_hour}:#{fuzzy_min / 10}~ (#{fuzzy_hour}:#{"%02d" % fuzzy_min}:#{"%02d" % fuzzy_sec})"
   end

end

if $0 == __FILE__
   t = FuzzyTime.new
   10.times do
     puts t, Time.new
     sleep 10
     t.update
   end
end

6

Ahh, it feels good to do a ruby quiz again :-). I've ignored the other
solutions so far so someone else may have taken the same approach.

I took the approach that there are actual 3 times involved, so as to
hopefully avoid as little as possible the range limiting that Ara was
talking about. And it just made it easier to think about the problem.

Essentially, the time displayed to the user is all that must be
increase. So long as that is continually moving forward, the times
behind the scene don't really matter. That for me results in 3
different times.

    - Actual time
    - Fuzzed time : actual time fuzzed within the fuzzy range (+- 5 min default)
    - Display time : Fuzzed time 'floored' to a granularity (10 min default)

As a result, my approach has the following algorithm:
    - Calculate the actual time (update/advance)
    - Calculate a fuzzy range for the new fuzzed time which has
        - lower bound = the maximum of the last display time or (actual - fuzz factor minutes)
        - upper bound = actual + range
    - randomly pick a new time in that range for the fuzzed time
    - calculate the new display time off of the fuzzed time

As a result, the Fuzzed time can increase/decrease with respect to
itself, but will always be greater than the displayed time. But overall
the fuzzed time will continue to increase. And the display time is
always increasing.

I also threw in some Extra Credits: 24hour/12hour option, fuzz factor
(changing the +- range) and display granularity(one minute, ten minute
on hour).

Great Quiz!

enjoy,

-jeremy

fuzzytime.rb (4.29 KB)

···

--

Jeremy Hinegardner jeremy@hinegardner.org

7

Hi,

attached is my FuzzyTime.rb solution and a corresponding Unit Test
file. Thanks for the quiz, I look forward to any feedback. I didn't
have time to do the extra credit tasks :frowning:

FuzzyTime.rb (2.25 KB)

FuzzyTimeTest.rb (4.9 KB)

···

On 10/27/06, Ruby Quiz <james@grayproductions.net> wrote:

The three rules of Ruby Quiz:

1. Please do not post any solutions or spoiler discussion for this quiz until
48 hours have passed from the time on this message.

2. Support Ruby Quiz by submitting ideas as often as you can:

http://www.rubyquiz.com/

3. Enjoy!

Suggestion: A [QUIZ] in the subject of emails about the problem helps everyone
on Ruby Talk follow the discussion. Please reply to the original quiz message,
if you can.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

by Gavin Kistner

        The Background
        ---------------------------------------------------------------------

Last night I was having trouble falling asleep, and was staring at my digital
alarm clock (as I do so often under that circumstance). Something on the bedside
table was occluding the minutes digit, however, so all I could tell is that it
was "10 4". (Oddly, my alarm clock has no ":" between the hours and minutes.)

"How nice!" I thought. "An imposed vagueness to keep me from obsessing on
exactly what time it is! Should I really be worried about the exact time?
Shouldn't I be more relaxed? Shouldn't a 10-minute precision in life be enough
to keep me roughly on time, without obsessing on exacting promptitude?"

I realized that if I kept staring at the clock (as I did), and I were to observe
it changing from "10 4" to "10 5", that I would, at that moment, know exactly
what time it is.

"Bah" I thought, "so much for that idea."

And then I thought some more. I thought of bad ideas: analog watches where the
hand erratically swings forward and backward, digital clocks that showed random
times near the correct time. And then I dreamed of the watch I wanted to own...

        The Challenge
        ---------------------------------------------------------------------

Requirement #1: Write a Ruby program that shows the current time, but only the
'tens' part of the minutes. For example, if the time is 10:37, then the program
might output "10:3~"

Requirement #2: The time shown by the clock must randomly vary +/- 5 minutes
from reality. For example, if the time is actually 10:37, the program might
output "10:3~" or "10:4~" (but not "10:2~" or "10:5~").

Requirement #3: The time on the clock should continuously increase. If the time
shows "10:4~" it must continue to show "10:4~" until it shows "10:5~". (It can't
show "10:4~", then "10:3~" for a bit and then come back to "10:4~".)

Putting the three requirements together, the left column below shows the actual
time and the next three columns show the possible outputs from three different
runs of the same program:

        10:35 10:3~ 10:4~ 10:3~
        10:36 10:3~ 10:4~ 10:3~
        10:37 10:3~ 10:4~ 10:3~
        10:38 10:3~ 10:4~ 10:3~
        10:39 10:4~ 10:4~ 10:3~
        10:40 10:4~ 10:4~ 10:3~
        10:41 10:4~ 10:4~ 10:3~
        10:42 10:4~ 10:4~ 10:3~
        10:43 10:4~ 10:4~ 10:3~
        10:44 10:4~ 10:4~ 10:3~
        10:45 10:4~ 10:4~ 10:4~
        10:46 10:4~ 10:4~ 10:5~
        10:47 10:4~ 10:4~ 10:5~
        10:48 10:4~ 10:4~ 10:5~
        10:49 10:4~ 10:4~ 10:5~
        10:50 10:4~ 10:4~ 10:5~
        10:51 10:4~ 10:4~ 10:5~
        10:52 10:5~ 10:4~ 10:5~
        10:53 10:5~ 10:4~ 10:5~
        10:54 10:5~ 10:4~ 10:5~
        10:55 10:5~ 10:5~ 10:5~
        10:56 10:5~ 10:5~ 11:0~
        10:57 10:5~ 10:5~ 11:0~
        10:58 10:5~ 10:5~ 11:0~
        10:59 10:5~ 10:5~ 11:0~
        11:00 10:5~ 10:5~ 11:0~
        11:01 10:5~ 10:5~ 11:0~

        Testing your Output
        ---------------------------------------------------------------------

You should supply a FuzzyTime class that supports the following:

        ft = FuzzyTime.new # Start at the current time
        ft = FuzzyTime.new(Time.at(1161104503)) # Start at a specific time

        p ft.to_s # to_s format
        #=> "10:5~"

        p ft.actual, ft.actual.class # Reports real time as Time
        #=> Tue Oct 17 11:01:36 -0600 2006
        #=> Time

        ft.advance( 60 * 10 ) # Manually advance time
        puts ft # by a specified number of
        #=> 11:0~ # seconds.

        sleep( 60 * 10 )

        ft.update # Automatically update the time based on the
        puts ft # time that has passed since the last call
        #=> 11:1~ # to #initialize, #advance or #update

Your class and output will be tested with code like the following:

        def test_output
          # Initialize with a well-known time
          ft = FuzzyTime.new( Time.at( ... ) )

          60.times do
            @legal = ... # Find the array of legal output strings
            @output = ft.to_s

            assert_block "#@output not one of #@legal.inspect" do
              @legal.include?( @output )
            end

            sleep( rand( 30 ) )
            ft.update
          end

          60.times do
            @legal = ... # Find the array of legal output strings
            @output = ft.to_s

            assert_block "#@output not one of #@legal.inspect" do
              @legal.include?( @output )
            end

            ft.advance( rand( 30 ) )
          end
        end

        Extra Credit
        ---------------------------------------------------------------------

        * Provide a self-running application that shows the time somehow.
        (ASCII in the terminal, some GUI window, etc.)

        * Allow your class to be customized to display 12- or 24-hour time.

        * Allow your class to be customized to change how close to reality
        it must display. (+/- 3 minutes, +/- 12 minutes, etc.)

        * Allow your class to be customized to change how roughly it displays
        the time (e.g. 1 minute, 10 minute, 1 hour intervals).

        * Ensure that the transition from one digit to the next occurs
        randomly across the range of -5 to +5. (So, while the digit might
        change 5 minutes before or 5 minutes after the real transition, on
        average the change should occur around the transition itself.)
        You might need to assume that your update/advance method will be
        called with a certain regularity (e.g. once per second, once every
        7 seconds, once every 30 seconds, etc.)

        * Come up with your own technique of displaying time that
        (a) is always 'close' to right, but (b) never allows a
        watchful person to ever know exactly what time it is.

        Things to Keep in Mind
        ---------------------------------------------------------------------

        * You need to be able to handle the transition across hour/day
        boundaries. (10:5~ might change to 11:0~ when the real time is still
        10:58, or might continue to display 10:5~ when the real time is
        11:04. On a 24-hour click, you also need to be able to wrap from
        23:5~ to 00:0~)

        * For testing purposes of the real-time #update advancing, you might
        find it easier to work with minutes and seconds instead of hours and
        minutes.

        * Requirement #3 is, well, a requirement. Repeated #update/#to_s
        calls to a FuzzyTime instance should never show an earlier time
        (unless 24 hours occurred between #update calls ;).

--
Caleb

"There is no theory of evolution, just a list of creatures Chuck
Norris allows to live."

8

Hi,

Here's my entry. I haven't peeked at any of the other responses yet, but I imagine most people have gone about this in roughly the same way. Any comments are welcome, I'm a relative nuby, and have only done toy projects so far.

The place where there's probably the most latitude for variation is in the algorithm for deciding how the offset between the reported time and the actual time varies. The first thing I tried was to figure out, whenever the time was updated, what the range of possible offsets was (given the current actual and reported times and need to make sure the reported time doesn't retrogress) and then select a new offset uniformly within that range. The problem there is that, if you update more often than every five minutes, the clock will tend to advance 4-5 minutes ahead of the actual time and stay there. To address that, I now select an offset uniformly within the range of allowable errors (+5 minutes to -5 minutes) and, if the new offset would cause the time to retrogress, I just leave the reported time unchanged. The offset will still tend to be positive, however, and more positive the shorter the interval between updates. I'm interested to see if anyone came up with a good way to get a balanced distribution of errors over a long run.

Cheers,

Tom

Here are my sources for the FuzzyTime module and a driver program. To run the driver, just say

     ruby fuzzyclock.rb

You can set the number of digits to fuzz out with the option '-f <ndigits>'.
You can set the "wobble" (maximum allowable error) with '-w <minutes>'.
You can have it display the actual time and cuurrent error with '-d'.
You can have it run in an accelerated test mode with the option '-t'.

- - - - - - - - - - - - - - - - - - - - fuzzytime.rb - - - - - - - - - - - - - - - - - - -
#!/usr/bin/env ruby
# Fuzzy time module
# Author: Tom Pollard <pollard@earthlink.net>

···

#
class FuzzyTime
   attr_reader :actual, :current, :updated
   attr_accessor :am_pm, :fuzz, :wobble, :method

   # Return a new FuzzyTime clock, intialized to the given time.
   # If no intial time is specified, the current time is used.
   # The default fuzz is 1 digit; the default wobble is 5 minutes;
   # times are represented in 12-hour style by default.
   #
   def initialize ( actual=nil )
     @actual = actual || Time.new() # the actual time (Time)
     @current = nil # the time that we report (Time)
     @updated = Time.new # when @current was last updated (Time)
     @wobble = 5 # the maximum error in @current (minutes)
     @fuzz = 1 # the number of digits to fuzz out (int)
     @method = 2 # the update algorithm to use (int)
     @am_pm = true # report 12-hour time? (boolean)
     @current = @actual + offset
   end

   # Advance the actual time by the given number of seconds
   # (The reported time may or may not change.)
   def advance ( delta=0 )
     @actual += delta
     @current = @actual + offset
     @updated = Time.new
     self
   end

   # Advance the actual time to account for the time since it was last changed.
   # (The reported time may or may not change.)
   def update
     advance( (Time.new - @updated).to_i )
   end

   # Calculate a new offset (in minutes) between the actual and reported times.
   # (This is called whenever the actual time changes.)
   def offset
     max_range = 2*@wobble + 1
     min_offset = @current.to_i/60 - @actual.to_i/60
     if @current.nil? || min_offset < -@wobble
       range = max_range
     else
       range = @wobble - min_offset + 1
     end
     range = max_range if range > max_range

     if range == 0
       delta = 0
     else
       if @method == 1
         # pick a new offset within the legal range of offsets.
         delta = @wobble - rand(range)
       else
         # pick a new offset within the range of allowable errors.
         # if it would require the time to regress, don't change the reported time.
         delta = @wobble - rand(max_range)
         delta = min_offset if delta < min_offset
       end
     end
     return 60 * delta
   end

   # Report the difference (in minutes) between the reported and actual times.
   def error
     (current - actual).to_i/60
   end

   # Return a string representation of the fuzzy time.
   # The number of digits obscured by tildes is controlled by the 'fuzz' attribute.
   # Whether the time is in 12- or 24-hour style is controlled by 'am_pm'.
   def to_s
     if @am_pm
       display = @current.strftime("%I:%M")
     else
       display = @current.strftime("%H:%M")
     end
     @fuzz.times { display.sub!(/\d(\D*)$/, '~\1') } if @fuzz > 0
     display
   end
end
- - - - - - - - - - - - - - - - - - - - fuzzyclock.rb - - - - - - - - - - - - - - - - - - -
#!/usr/bin/env ruby
#
# Report the current time on the console, using the FuzzyTime module.
#
require 'fuzzytime.rb'
require 'getoptlong.rb'

opts = GetoptLong.new(
   [ '--fuzz', '-f', GetoptLong::REQUIRED_ARGUMENT],
   [ '--wobble', '-w', GetoptLong::REQUIRED_ARGUMENT],
   [ '--24hour', '-m', GetoptLong::NO_ARGUMENT],
   [ '--test', '-t', GetoptLong::NO_ARGUMENT],
   [ '--debug', '-d', GetoptLong::NO_ARGUMENT]
)

ft = FuzzyTime.new
test = false
debug = false

opts.each do |opt, arg|
   ft.fuzz = arg.to_i if opt == '--fuzz'
   ft.wobble = arg.to_i if opt == '--wobble'
   ft.am_pm = false if opt == '--24hour'
   debug = true if opt == '--debug'
   test = true if opt == '--test'
end

puts "Fuzzy Clock"
while true
   printf "\r%s", ft.to_s
   printf " (%s %3d)", ft.actual.strftime("%H:%M"), ft.error if debug
   STDOUT.flush
   if test
     sleep 1
     ft.advance 60
   else
     sleep 60
     ft.update
   end
end
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

9

it seems like #2 and #3 contradict one another.

Indeed. I take it that the challenge of the quiz is to come up with a
way to balance out the two goals. The purpose for requirement 2 is
that you don't want the user to be able to deduce the actual time
based on when you switch from one output to the next. The problem
with doing that as a simple random selection is that you get wildly
differing ranges.

+/- 5 minutes from reality.

Is problematic, as you point out Ara. The example

For example, if the time is actually 10:37, the program might
output "10:3~" or "10:4~" (but not "10:2~" or "10:5~").

however, is much more lenient. You don't have to round down, you just
can't pick a number from a different section. (10:3~ is not +/-5 of
10:37 obviously).

I gather that there would be some pretty simple ways you can dampen
the latter effect while still preventing the user from easily guessing
the actual time.

···

On 10/27/06, ara.t.howard@noaa.gov <ara.t.howard@noaa.gov> wrote:

--
Lou.

10

Then let me be one of the first to welcome you to Ruby and the Ruby Quiz!

James Edward Gray II

···

On Oct 29, 2006, at 10:28 AM, Marcel Ward wrote:

This is also my first greeting to the Ruby community... Hello!

11

Hi all,

This is my first submission to the list and I'm new to Ruby too. I'm finding the quiz excellent for learning. Comments and advice would really be appreciated.

I haven't had time to do any "extra credit" stuff, or even test this fully, but here goes -

class FuzzyTime

   attr_reader :actual, :display

   def initialize(*start_time)
     @current_systime = Time.new
     @actual = start_time[0] || Time.new
     @last_displayed = @actual
   end

   def to_s
     # Decide whether to go forward or back 5 mins
     if rand(2) == 1
       @display = @actual + (5 * 60)
     else
       @display = @actual - (5 * 60)
     end

     # If the time we are going to display is before what was last displayed, don't do it
     if @display < @last_displayed
       @display = @last_displayed
     end

     @last_displayed = @display

     "#{"%02d" % @display.hour}:#{("%02d" % @display.min.to_s)[0..0]}~"
   end

   # Advance the actual time by a number of seconds, reset the system time record so that
   # update will work
   def advance(secs)
     @actual += secs
     @current_systime = Time.new
   end

   # Work out the relative time difference since the last initialize, advance or update
   # and apply this to the actual time
   def update
     diff = Time.new - @current_systime
     @actual += diff.to_i
     @current_systime = Time.new
   end

end

Thanks everyone

Robert

12

Hi all,

I'm new to Ruby and this is the first quiz I'm doing. Not sure if I'm
missing something, but this seems pretty easy to me. Here's what I
have:

class FuzzyTime
  # if 24 then show in 24 hour format, else 12 hour format
  attr_accessor :mode

  def initialize(startAt = Time.now, variance = 5*60)
    @time = Time.at(startAt)
    @offset = Time.now - @time
    @variance = variance
    @mintime = Time.at(@time.to_i - @variance).to_i
    @mode = 24
  end

  def to_s
    t = @time.to_i - @variance + rand(@variance * 2)
    @mintime = @mintime > t ? @mintime : t
    now = Time.at(@mintime)
    sprintf('%02d:%d~ %s',
      @mode == 24 ? now.hour : now.hour % 12,
      now.min / 10,
      @mode != 24 ? now.hour / 12 == 1 ? 'pm' : 'am' : ''
    )
  end

  def update
    @time = Time.now + @offset
  end

  def actual
    @time
  end

  # def advance(amt)
  def +(amt)
    @time = @time + amt
    self
  end

  def -(amt)
    @time = @time + (-amt)
    # reset the minimum displayed time
    @mintime = Time.at(@time.to_i - @variance).to_i
    self
  end
end

if __FILE__ == $0 then
  t = FuzzyTime.new
  t.mode = 24

  30.times {
    t += 60
    puts "#{t.to_s} (#{t.actual.strftime('%H:%M')})"
  }
end

Any comments are welcome.

Cheers,
Thomas

···

2006/10/30, Caleb Powell <caleb.powell@gmail.com>:

Hi,

attached is my FuzzyTime.rb solution and a corresponding Unit Test
file. Thanks for the quiz, I look forward to any feedback. I didn't
have time to do the extra credit tasks :frowning:

On 10/27/06, Ruby Quiz <james@grayproductions.net> wrote:
> The three rules of Ruby Quiz:
>
> 1. Please do not post any solutions or spoiler discussion for this quiz until
> 48 hours have passed from the time on this message.
>
> 2. Support Ruby Quiz by submitting ideas as often as you can:
>
> http://www.rubyquiz.com/
>
> 3. Enjoy!
>
> Suggestion: A [QUIZ] in the subject of emails about the problem helps everyone
> on Ruby Talk follow the discussion. Please reply to the original quiz message,
> if you can.
>
> -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>
> by Gavin Kistner
>
> The Background
> ---------------------------------------------------------------------
>
> Last night I was having trouble falling asleep, and was staring at my digital
> alarm clock (as I do so often under that circumstance). Something on the bedside
> table was occluding the minutes digit, however, so all I could tell is that it
> was "10 4". (Oddly, my alarm clock has no ":" between the hours and minutes.)
>
> "How nice!" I thought. "An imposed vagueness to keep me from obsessing on
> exactly what time it is! Should I really be worried about the exact time?
> Shouldn't I be more relaxed? Shouldn't a 10-minute precision in life be enough
> to keep me roughly on time, without obsessing on exacting promptitude?"
>
> I realized that if I kept staring at the clock (as I did), and I were to observe
> it changing from "10 4" to "10 5", that I would, at that moment, know exactly
> what time it is.
>
> "Bah" I thought, "so much for that idea."
>
> And then I thought some more. I thought of bad ideas: analog watches where the
> hand erratically swings forward and backward, digital clocks that showed random
> times near the correct time. And then I dreamed of the watch I wanted to own...
>
> The Challenge
> ---------------------------------------------------------------------
>
> Requirement #1: Write a Ruby program that shows the current time, but only the
> 'tens' part of the minutes. For example, if the time is 10:37, then the program
> might output "10:3~"
>
> Requirement #2: The time shown by the clock must randomly vary +/- 5 minutes
> from reality. For example, if the time is actually 10:37, the program might
> output "10:3~" or "10:4~" (but not "10:2~" or "10:5~").
>
> Requirement #3: The time on the clock should continuously increase. If the time
> shows "10:4~" it must continue to show "10:4~" until it shows "10:5~". (It can't
> show "10:4~", then "10:3~" for a bit and then come back to "10:4~".)
>
> Putting the three requirements together, the left column below shows the actual
> time and the next three columns show the possible outputs from three different
> runs of the same program:
>
> 10:35 10:3~ 10:4~ 10:3~
> 10:36 10:3~ 10:4~ 10:3~
> 10:37 10:3~ 10:4~ 10:3~
> 10:38 10:3~ 10:4~ 10:3~
> 10:39 10:4~ 10:4~ 10:3~
> 10:40 10:4~ 10:4~ 10:3~
> 10:41 10:4~ 10:4~ 10:3~
> 10:42 10:4~ 10:4~ 10:3~
> 10:43 10:4~ 10:4~ 10:3~
> 10:44 10:4~ 10:4~ 10:3~
> 10:45 10:4~ 10:4~ 10:4~
> 10:46 10:4~ 10:4~ 10:5~
> 10:47 10:4~ 10:4~ 10:5~
> 10:48 10:4~ 10:4~ 10:5~
> 10:49 10:4~ 10:4~ 10:5~
> 10:50 10:4~ 10:4~ 10:5~
> 10:51 10:4~ 10:4~ 10:5~
> 10:52 10:5~ 10:4~ 10:5~
> 10:53 10:5~ 10:4~ 10:5~
> 10:54 10:5~ 10:4~ 10:5~
> 10:55 10:5~ 10:5~ 10:5~
> 10:56 10:5~ 10:5~ 11:0~
> 10:57 10:5~ 10:5~ 11:0~
> 10:58 10:5~ 10:5~ 11:0~
> 10:59 10:5~ 10:5~ 11:0~
> 11:00 10:5~ 10:5~ 11:0~
> 11:01 10:5~ 10:5~ 11:0~
>
> Testing your Output
> ---------------------------------------------------------------------
>
> You should supply a FuzzyTime class that supports the following:
>
> ft = FuzzyTime.new # Start at the current time
> ft = FuzzyTime.new(Time.at(1161104503)) # Start at a specific time
>
> p ft.to_s # to_s format
> #=> "10:5~"
>
> p ft.actual, ft.actual.class # Reports real time as Time
> #=> Tue Oct 17 11:01:36 -0600 2006
> #=> Time
>
> ft.advance( 60 * 10 ) # Manually advance time
> puts ft # by a specified number of
> #=> 11:0~ # seconds.
>
> sleep( 60 * 10 )
>
> ft.update # Automatically update the time based on the
> puts ft # time that has passed since the last call
> #=> 11:1~ # to #initialize, #advance or #update
>
> Your class and output will be tested with code like the following:
>
> def test_output
> # Initialize with a well-known time
> ft = FuzzyTime.new( Time.at( ... ) )
>
> 60.times do
> @legal = ... # Find the array of legal output strings
> @output = ft.to_s
>
> assert_block "#@output not one of #@legal.inspect" do
> @legal.include?( @output )
> end
>
> sleep( rand( 30 ) )
> ft.update
> end
>
> 60.times do
> @legal = ... # Find the array of legal output strings
> @output = ft.to_s
>
> assert_block "#@output not one of #@legal.inspect" do
> @legal.include?( @output )
> end
>
> ft.advance( rand( 30 ) )
> end
> end
>
> Extra Credit
> ---------------------------------------------------------------------
>
> * Provide a self-running application that shows the time somehow.
> (ASCII in the terminal, some GUI window, etc.)
>
> * Allow your class to be customized to display 12- or 24-hour time.
>
> * Allow your class to be customized to change how close to reality
> it must display. (+/- 3 minutes, +/- 12 minutes, etc.)
>
> * Allow your class to be customized to change how roughly it displays
> the time (e.g. 1 minute, 10 minute, 1 hour intervals).
>
> * Ensure that the transition from one digit to the next occurs
> randomly across the range of -5 to +5. (So, while the digit might
> change 5 minutes before or 5 minutes after the real transition, on
> average the change should occur around the transition itself.)
> You might need to assume that your update/advance method will be
> called with a certain regularity (e.g. once per second, once every
> 7 seconds, once every 30 seconds, etc.)
>
> * Come up with your own technique of displaying time that
> (a) is always 'close' to right, but (b) never allows a
> watchful person to ever know exactly what time it is.
>
> Things to Keep in Mind
> ---------------------------------------------------------------------
>
> * You need to be able to handle the transition across hour/day
> boundaries. (10:5~ might change to 11:0~ when the real time is still
> 10:58, or might continue to display 10:5~ when the real time is
> 11:04. On a 24-hour click, you also need to be able to wrap from
> 23:5~ to 00:0~)
>
> * For testing purposes of the real-time #update advancing, you might
> find it easier to work with minutes and seconds instead of hours and
> minutes.
>
> * Requirement #3 is, well, a requirement. Repeated #update/#to_s
> calls to a FuzzyTime instance should never show an earlier time
> (unless 24 hours occurred between #update calls ;).
>

--
Caleb

"There is no theory of evolution, just a list of creatures Chuck
Norris allows to live."

13

Here is my script. This is my first entry to Ruby Quiz.

I wanted this FuzzyTime to support random access so you can do this:

ft = FuzzyTime.new; puts ft
=> 17:5~
ft = FuzzyTime.set(Time.now+4.hours); puts ft
=> 22:0~
ft = FuzzyTime.set(Time.now+10.minutes); puts ft
=> 18:1~
ft = FuzzyTime.set(Time.now); puts ft
=> 17:5~

Also, I added a 'rewind' method for symmetry with 'advance' (although
you cannot rewind to before the time FuzzyTime was initialized with).
Now 'update' adds to the internal time based on how long since you last
called one of 'initialize', 'advance', 'rewind', 'update' or 'set'.

Other than ensuring that the transition occurs randomly for each ten
minute block, I didn't implement any of the extra credit options.

-Dan Lucraft

···

___________________________________________________

# handy stuff...
require
'/home/dan/gems/activesupport-1.3.1/lib/active_support/core_ext/numeric'
require
'/home/dan/gems/activesupport-1.3.1/lib/active_support/core_ext/time'

class FuzzyTime
  def initialize(time=Time.now)
    # we record the start time as it's used to reset the random number
generator
    # every time we fuzzify a time
    @start_time = time

    time_mins = (time - time.beginning_of_day).to_i/60
    hours = time_mins/60
    mins = time_mins-(hours*60)
    tens = mins/10
    @time_of_nearest_ten_before_start = time_mins - mins + (tens*10) -5

    @internal_time = time
    @last_called = time
  end

  def actual
    @internal_time
  end

  def advance(secs)
    @internal_time += secs
    @last_called = Time.now
  end

  def rewind(secs)
    @internal_time -= secs
    check_valid
    @last_called = Time.now
  end

  def update
    @internal_time += Time.now - @last_called
    check_valid
    @last_called = Time.now
  end

  def set(time=Time.now)
    @internal_time = time
    check_valid
    @last_called = Time.now
  end

  # this fuzzifies the current internal time.
  def to_s
    # run through random numbers for the number of 10 minute blocks
since the
    # start time, and keep the last one (switch_val)
    time_mins = ((@internal_time -
@start_time.beginning_of_day).to_i)/60
    distance = time_mins - @time_of_nearest_ten_before_start
    Kernel.srand(@start_time.to_i)
    switch_val = nil
    ((distance/10)+1).to_i.times do
      switch_val = rand(10)
    end

    # the kept random number is where in the 10 minute interval around
    # the current time that the fuzzy time switches from low to high
    # E.g.
    # current time 9:12
    # interval around current time: [9:05, 9:15]
    # a switch_val of 3 means that we go from 9:0~ to 9:1~ at 9:08
    # NB we always get the same switch_val for this ten-minute block,
    # since we are resetting the generator and counting the correct
number
    # of random numbers in. This is what allows random access.
    # marginal_mins is 7 in this case. (9:12-9:05)
    marginal_mins = distance - (10*(distance/10))
    if marginal_mins >= switch_val and marginal_mins >= 5
      near_time(@internal_time, :below)
    elsif marginal_mins >= switch_val and marginal_mins < 5
      near_time(@internal_time, :above)
    elsif marginal_mins < switch_val and marginal_mins >= 5
      near_time(@internal_time-10.minutes, :below)
    elsif marginal_mins < switch_val and marginal_mins < 5
      near_time(@internal_time, :below)
    end
  end

  def near_time(time, type)
    time = (time - time.beginning_of_day).to_i
    hour = time/3600
    fuzzy_min = ((time - (hour*3600))/60)/10
    fuzzy_min += 1 if type == :above
    (fuzzy_min = 0 and hour += 1) if fuzzy_min == 6
    hour = 0 if hour == 24
    if hour >= 10
      "#{hour}:#{fuzzy_min}~"
    else
      "0#{hour}:#{fuzzy_min}~"
    end
  end

  def check_valid
    if @internal_time < @start_time
      raise Exception, "Rewound past start of FuzzyTime."
    end
  end
end

if __FILE__ == $0
  ft = FuzzyTime.new
  puts ft
  step = ARGV[0].to_i || 60
  while(true)
    sleep step
    ft.advance 60
    puts ft
  end
end

--
Posted via http://www.ruby-forum.com/.

14

I implemented a third method for updating the offset that produces a relatively balanced distribution of errors, and added some statistics-gathering to my driver script. Here are some comparisons of the three update methods, tested by running 100000 60-second 'advances' with each method. The numbers represent the percentage of the time that each error was found. (The 'error', again, is the reported time minus the actual time, in minutes.)

Method 1
* Choose offset uniformly from the set of values that prevent the reported time from regressing.

-5 -4 -3 -2 -1 0 1 2 3 4 5
0.0 0.0 0.0 0.0 0.1 0.3 1.6 6.2 18.4 36.5 36.9

Method 2
* Choose offset uniformly from the set of all allowable offsets, but don't change the reported time if the chosen offset would cause it to retrogress.

-5 -4 -3 -2 -1 0 1 2 3 4 5
0.0 0.1 0.7 2.2 5.5 10.2 15.7 19.7 20.3 16.6 9.0

Method 3
* Changes offset randomly by +/- one minute on each update, but don't change the reported time if the chosen offset would cause it to retrogress.

-5 -4 -3 -2 -1 0 1 2 3 4 5
9.2 9.4 9.6 9.3 9.1 8.8 9.1 9.0 8.8 8.8 9.0

I've attached the updated scripts. The driver has number of new options (see the usage message in the script).
To generate the statistics shown above, you'd say, for instance.

     fuzzyclock -t -q -n 100000 -m 1

To see how the offset changes, you could say

     fuzzyclock -d -m 2

Hopefully it's reasonably self-explanatory.

Tom

fuzzytime.rb (3.32 KB)

fuzzyclock.rb (2.49 KB)

···

On Oct 30, 2006, at 1:30 PM, Tom Pollard wrote:

[...] in the algorithm for deciding how the offset between the reported time and the actual time varies. The first thing I tried was to figure out, whenever the time was updated, what the range of possible offsets was (given the current actual and reported times and need to make sure the reported time doesn't retrogress) and then select a new offset uniformly within that range. The problem there is that, if you update more often than every five minutes, the clock will tend to advance 4-5 minutes ahead of the actual time and stay there. To address that, I now select an offset uniformly within the range of allowable errors (+5 minutes to -5 minutes) and, if the new offset would cause the time to retrogress, I just leave the reported time unchanged. The offset will still tend to be positive, however, and more positive the shorter the interval between updates. I'm interested to see if anyone came up with a good way to get a balanced distribution of errors over a long run.

15

Hi all

Here's is my script. It was fun working at it, just please no more
time based quiz when there's the switching of daylight time saving :stuck_out_tongue:
The scripts defines two class one to manage how to move within a given
range and one for actual FuzzyTime implementation.
At the end of the email there's a really ugly extra file you may want
to use to play with the FuzzyTime class.

Paolo

#!/bin/ruby
class WanderingWalker
  SIGN = [1, -1]
  CHECK_LIMIT = %w(min max)
  DEFAULT_GENERATOR = lambda { |limit| rand(limit) * SIGN[rand(2)] }
  attr_reader :position, :limit, :target
  alias :level :position
  def initialize(limit, &block)
    @limit = limit
    @generator = block_given? ? block : DEFAULT_GENERATOR
    @position = 0
    generate_target
  end
  def walk(steps)
    generate_target while @position == @target
    new_pos = [(@position + direction*steps), @target].send \
      CHECK_LIMIT[SIGN.index(direction)]
    @position = new_pos
  end
  def distance
    @target - @position
  end
  def direction
    if distance == 0 : 1 else distance/distance.abs end
  end
  private
  def generate_target
    @target = @generator.call limit
  end
end

class FuzzyTime
  FORMATS = %w(%H:%M %I:%M)
  attr_reader :fuzziness
  #two params, both optional time and an hash
  #time: a time object used as the starting point
  #hash params
  #:hidden_digits - hidden_digits number, from right
  #:precision - maximum distance from real time in seconds
  def initialize(time=Time.new, opts={})
    @internaltime = time
    @last_call = @printed_time = Time.new
    @precision = opts[:precision] || 300
    @fuzziness = WanderingWalker.new(@precision)
    @format = FORMATS[0]
    @hidden_digits = opts[:hidden_digits] || 1
    @sub_args = case @hidden_digits
      when 0 : [//, '']
      when 1 : [/\d$/, '~']
      when 2 : [/\d{2}$/, '~~']
      when 3 : [/\d:\d{2}$/, '~:~~']
      else
        raise "nothing to see!"
    end
  end
  def advance(secs)
    tic(secs)
  end
  def update
    tic Time.new - @last_call
  end
  def actual
    @internaltime
  end
  #switch 12 / 24h format
  def toggle_format
    @format = FORMATS[FORMATS.index(@format) == 0 ? 1 : 0]
  end
  def to_s
    @printed_time = [@printed_time, (@internaltime + fuzziness.level)].max
    @printed_time.strftime(@format).sub(*@sub_args)
  end
  private
  def tic(secs=1)
    @internaltime += secs
    @last_call = Time.new
    @fuzziness.walk secs
  end
end

Ad here's the super ugly runner script

#!/bin/ruby
require 'fuzzy_time'
# accepts a FuzzyTime object as argument + an hash of options
#possible options
# :time_warp if true instead of working as a clock just prints out
#in an instant all the clock output, if false, works as a clock
# :step_size how often the clock will be updated in seconds
# :print_actual prints the actual time
# :print_fuzziness, prints the error size
# :toggle switch at every step from 24 to 12 hour format
# :duration how many step_size the clock should run
class FuzzyExec
  def initialize(ft = FuzzyTime.new ,opts = {})
    opt_def = {:duration => 100, :step_size => 60, :print_actual => true}
    @opts = opt_def.update opts
    @ft = ft
  end
  def show_fuzzy_clock
    @opts[:duration].times do
      @ft.toggle_format if @opts[:toggle]
      out = []
      out << @ft.to_s
      out << @ft.actual.strftime('%H:%M') if @opts[:print_actual]
      out << @ft.fuzziness.level if @opts[:print_fuzziness]
      out << Time.new.strftime('%H:%M') if @opts[:print_current]
      puts out.join ' '
      if @opts[:time_warp]
        @ft.advance(@opts[:step_size])
      else
        sleep @opts[:step_size]
        @ft.update
      end
    end
  end
end

16

Hi all,

Hello.

This is my first submission to the list and I'm new to Ruby too.

Welcome!

Comments and advice would really be appreciated.

My comment is that I wish I wrote Ruby that pretty when I was new. :slight_smile:

I'll give a couple super minor suggestions...

  def initialize(*start_time)
    @current_systime = Time.new
    @actual = start_time[0] || Time.new
    @last_displayed = @actual
  end

Why take an Array of arguments but only use the first one? I think you should drop the slurping operator:

def initialize(start_time)
   @current_systime = Time.new
   @actual = start_time || Time.new
   @last_displayed = @actual
end

    # Decide whether to go forward or back 5 mins
    if rand(2) == 1
      @display = @actual + (5 * 60)
    else
      @display = @actual - (5 * 60)
    end

You could shorten that up a bit, though I'm not sure this is as readable:

@display = @actual.send(%w[+ -][rand(2)], 5 * 60)

    "#{"%02d" % @display.hour}:#{("%02d" % @display.min.to_s)[0..0]}~"

Perhaps the this is more straight forward:

@display.strftime("%H:%M").sub(/\d$/, "~")

Hope that gives you some new ideas.

James Edward Gray II

···

On Oct 29, 2006, at 6:34 PM, Robert Conn wrote:

17

Thanks for the test and the quiz. Writing a solution wasn't very hard,
but coming up with a good way to keep the time from drifting ahead and
had good 'fuzziness', quantifying what made a good fuzzy time and then
testing different approaches was the interesting part.

An approach I took to test the fuzziness of my FuzzyTime class was
track the number of minutes the fuzzy time remained the same, advancing
one minute at a time, and then calculate the mean and variance of that
set of numbers, with the idea that a good fuzzy time would have a mean
change interval close to 10 minutes but with a large variance. That
would also snag solutions that always displayed the correct time plus
solutions that were always ahead or behind by a fixed amount: there
would be no variance to the intervals. (It would also be good to see
different results each time it's run) A unit test for that is after my
solution.

In my approach, when a time is asked for, it computes a time that is
+/- 5 minutes from the actual time, keeping a low water mark that is
the last displayed time or 5 mintes from the actual time, whatever is
greater. There is a strong bias not to advance the time, correcting for
the tendancy for the time to drift ahead. This is what my solution got
running your test:

Variation: 10.37% ahead, 20.75% behind
Variation: 13.73% ahead, 8.39% behind
Variation: 13.46% ahead, 10.64% behind
Variation: 13.16% ahead, 10.72% behind
Variation: 13.27% ahead, 11.64% behind
Variation: 13.96% ahead, 9.06% behind
Variation: 13.76% ahead, 9.87% behind
Variation: 13.43% ahead, 10.57% behind
Variation: 13.69% ahead, 8.77% behind
Variation: 13.54% ahead, 9.18% behind
Variation: 13.18% ahead, 9.73% behind
Variation: 13.11% ahead, 10.15% behind
Variation: 13.00% ahead, 10.67% behind
Variation: 13.00% ahead, 10.30% behind
Variation: 12.92% ahead, 10.57% behind
Variation: 12.64% ahead, 10.80% behind
Variation: 12.64% ahead, 11.07% behind
Variation: 12.52% ahead, 10.94% behind
Variation: 12.39% ahead, 11.28% behind
Variation: 12.33% ahead, 11.49% behind

And means and variances:

Mean interval: 9.02446115288221
Variance: 3.07336219244858

As for the solution:

---- FuzzyTime.rb

# Fuzzy Time class that reports a time that is always within a given
# slop factor to the real time. The user specifies the amount of
# fuzzyiness to the time and the display obscures the minutes field.

···

#
# This class works by maintaining the actual time it represents, and
# calculating a new fuzzy time whenever it is asked to display the
# fuzzy time. It keeps a low water mark so an earlier time is never
# displayed.
#
class FuzzyTime
  # Initialize this object with a known time and a number of minutes
  # to randomly vary
  #
  # time -> initial time
  # fuzzy_minutes -> number of minutes to randomly vary time
  def initialize(time=Time.now, fuzzy_minutes=5)
    @fuzzy_factor = fuzzy_minutes
    @current_time = time
    set_low_water_mark
    set_updated
  end

  # Print the fuzzy time in a format obscuring the last number of the
  # time.
  def to_s
    ft = fuzzy_time
    s = ft.strftime("%H:%M")
    s[4] = '~'
    s
  end

  # Manually advance time by a certain number of seconds. Seconds
  # cannot be negative
  #
  # seconds -> number of seconds to advance. Will throw exception
  # if negative
  def advance(seconds)
    raise "advance: seconds cannot be negative" if seconds < 0
    @current_time = @current_time + seconds
    set_updated
  end

  # Update the current time with the number of seconds that has
  # elapsed since the last time this method was called
  def update
    @current_time = @current_time + update_interval
    set_updated
  end

  # Reports real time as Time
  def actual
    @current_time
  end

private
  # sets the current low water mark. This is so the fuzzy time never
  # goes backwards
  def set_low_water_mark
    @low_water_mark = @current_time - (@fuzzy_factor*60)
  end

  # Updates the last time initialize, advance or update was called
  def set_updated
    @last_updated = Time.now
  end

  # Gets the number of seconds since the last update
  def update_interval
    Time.now - @last_updated
  end

  # Sets fuzzy time to be +/- the fuzzy factor from the current time,
  # while ensuring that we never return an earlier time than the one
  # returned last time we were called.
  def fuzzy_time
    fuzzy_seconds = @fuzzy_factor * 60

    # Raise the low watermark if it is lower than allowed, if we
    # advanced by a huge degree, etc.
    @low_water_mark =
      [@low_water_mark, @current_time - fuzzy_seconds].max

    # Compute a new random time, and set it to be the fuzzy time if
    # it is higher than the low water mark. The algorithm is biased
    # to return a negative time. This is to compensate for the low
    # water mark. We want the time to be behind as much as it is
    # ahead. At least 60 percent of the time the time will not
    # advance here.
    random_time = @current_time +
      (rand(fuzzy_seconds*5) - fuzzy_seconds*4)
    fuzzy_time = [@low_water_mark, random_time].max

    # Update the low water mark if necessary
    @low_water_mark = [@low_water_mark, fuzzy_time].max

    fuzzy_time
  end
end

-----

The unit test to calculate means and variances:

----- FuzzyTimeTest.rb

require 'FuzzyTime'

class FuzzyTimeTest < Test::Unit::TestCase
  # Advances the fuzzy time by one minute repeatedly, keeping track
  # of how many minutes it took to go to the next time on the clock.
  # Calculates mean and variance to see if the intervals center
  # around 10 minutes and how much they vary from the mean. We want
  # the average to hover close to 10 minutes and the variance to be
  # as large as possible.
  def test_intervals
    ft = FuzzyTime.new

    last_time = nil
    fuzzy_interval = 0
    intervals = Array.new
    100000.times do
      ft.advance 60
      fuzzy_time = ft.to_s

      if last_time.nil? || last_time == fuzzy_time
        fuzzy_interval += 1
      else
        intervals.push fuzzy_interval
        fuzzy_interval = 0
      end
      last_time = fuzzy_time
    end

    average = intervals.inject {|sum,val| sum + val }.to_f /
      intervals.length
    puts "Mean interval: #{average}"

    variance = intervals.inject {|sum, val| sum+(val-average).abs}.to_f
/
      intervals.length
    puts "Variance: #{variance}"
  end
end

18

Welcome!

James Edward Gray II

···

On Oct 30, 2006, at 12:43 PM, Daniel Lucraft wrote:

This is my first entry to Ruby Quiz.

19

Here are some comparisons of the three update methods, tested by running 100000 60-second 'advances' with each method. The numbers represent the percentage of the time that each error was found. (The 'error', again, is the reported time minus the actual time, in minutes.)

Out of curiosity, I tried translating Cameron's method into my code. (This mainly involved working in units of minutes, rather than seconds). I found it produces the following distribution,

Cameron's method
* Choose offset uniformly from the set [-5..1], , but don't change the reported time if the chosen offset would cause it to retrogress.
-5 -4 -3 -2 -1 0 1 2 3 4 5
0.0 1.2 7.2 18.1 28.4 28.3 16.7 0.0 0.0 0.0 0.0

The results are reasonably balanced, centered more-or-less symmetrically around minus a half-minute.
Also, in this scheme, the reported time can /never/ be more than one minute ahead of the actual time.

I wanted to do this with other people's entries, too, but am out of time for now...

Cheers,

Tom

···

On Oct 31, 2006, at 1:05 AM, Tom Pollard wrote:

Method 1
* Choose offset uniformly from the set of values that prevent the reported time from regressing.

-5 -4 -3 -2 -1 0 1 2 3 4 5
0.0 0.0 0.0 0.0 0.1 0.3 1.6 6.2 18.4 36.5 36.9

Method 2
* Choose offset uniformly from the set of all allowable offsets, but don't change the reported time if the chosen offset would cause it to retrogress.

-5 -4 -3 -2 -1 0 1 2 3 4 5
0.0 0.1 0.7 2.2 5.5 10.2 15.7 19.7 20.3 16.6 9.0

Method 3
* Changes offset randomly by +/- one minute on each update, but don't change the reported time if the chosen offset would cause it to retrogress.

-5 -4 -3 -2 -1 0 1 2 3 4 5
9.2 9.4 9.6 9.3 9.1 8.8 9.1 9.0 8.8 8.8 9.0

20

Hi

I've posted an old version the second line of initialize should be changed from

@last_call = @printed_time = Time.new

to

@last_call = @printed_time = time

sorry

Paolo