Can anyone try to solve this problems?

ruby-talk
21

Hi,

At Tue, 16 Jan 2007 13:07:47 +0900,
Peña, Botp <botp@delmonte-phil.com> wrote in [ruby-talk:234253]:

Hi Nobu, will the &: notation/feature be incorporated in 1.8.x series?

I don't think so, but Symbol#to_proc was incorporated from
ActiveSupport.

···

--
Nobu Nakada

22

Daniel Martin wrote:

Why build up a separate hash structure?

It's simpler to my eyes. It's also (admittedly unintuitively) faster
though.

Here's a quick test with your version, my original, and another going
off your idea, but I tried to simplify it a bit:

#!/opt/local/bin/ruby
class Symbol
  def to_proc
    lambda { |x| x.send(self) }
  end
end

module Enumerable
  def max_by1
    last_value = nil

    inject do |max_item, item|
      current_value = yield item
      if last_value.nil? || current_value > last_value
        last_value = current_value
        item
      else
        max_item
      end
    end
  end

  def max_by2
    pairs = inject({}) do |hash, obj|
      hash[yield obj] = obj; hash
    end
    pairs[pairs.keys.max]
  end

  def max_by3
    max_value = nil
    max_item = nil

    each do |item|
      value = yield(item)
      max_item, max_value = item, value if max_value.nil? || value > max_value
    end

    max_item
  end
end

a = %w{ one two three four }

16.times do |i|
  a = a + a
end

puts "a.size => #{a.size}"
require 'benchmark'

Benchmark::bm do |bm|
  bm.report { puts a.max_by1 &:size }
  bm.report { puts a.max_by2 &:size }
  bm.report { puts a.max_by3 &:size }
end

I couldn't tell you why the 3rd is so much faster than the first. Just
goes to prove the old programming adage though: "Optimizing before
Profiling is a waste of time."

Not that this counts as serious profiling of course. :slight_smile: