Generate binary sequences of length n?

ruby-talk
1

I'm rather new to Ruby. I feel this should be very simple, but I'm
having trouble:

I'd like to write a script to work through all possible binary sequences
of length n.

The script would work as follows:

mylength = 4
resultz = binary_seq_generator(mylength)
puts "#{resultz}"

#resultz, not necessarily in this order:
["0000","0001","0010","0011","0100","0101","0110","0111","1000","1001","1010","1011","1100","1101","1110","1111"]

Important to my use: This binary_seq_generator method must be written
in such a way so that each subsequent member of the resultz array would
be completely generated before the next member starts. This is where
I'm stuck. I have trying manipulating the graycode algorithm here:
http://yagni.com/graycode/

This graycode algorithm seems to produce an array where each member is
only finalized on the final recurse. I may be wrong...but by this
method, I can't use resultz[i] for something before the algorithm starts
to build resultz[i+1], and I need to use each member of the resultz
array before moving on to the next binary string in the sequence.

Thanks much for helping a newbie!

···

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

2

Hi --

I'm rather new to Ruby. I feel this should be very simple, but I'm
having trouble:

I'd like to write a script to work through all possible binary sequences
of length n.

The script would work as follows:

mylength = 4
resultz = binary_seq_generator(mylength)
puts "#{resultz}"

#resultz, not necessarily in this order:
["0000","0001","0010","0011","0100","0101","0110","0111","1000","1001","1010","1011","1100","1101","1110","1111"]

Try this:

def binary_seq_generator(n)
   (0...(1 << n)).map {|e| "%0#{n}d" % e.to_s(2) }
end

Doesn't necessarily roll off the fingers as readily as some Ruby
idioms do :slight_smile: But I think all or most of what you need is there, and
there are some interesting bits to it.

David

···

On Mon, 10 Aug 2009, Tom Best wrote:

--
David A. Black / Ruby Power and Light, LLC / http://www.rubypal.com
Q: What's the best way to get a really solid knowledge of Ruby?
A: Come to our Ruby training in Edison, New Jersey, September 14-17!
    Instructors: David A. Black and Erik Kastner
    More info and registration: http://rubyurl.com/vmzN

3

Well 1.9 has to offer some elegance here

(1<<n).times.map{ | d | "%0{n}b" % d }

HTH
Robert

···

On Sun, Aug 9, 2009 at 8:32 PM, David A. Black<dblack@rubypal.com> wrote:

Hi --

On Mon, 10 Aug 2009, Tom Best wrote:

I'm rather new to Ruby. I feel this should be very simple, but I'm
having trouble:

I'd like to write a script to work through all possible binary sequences
of length n.

The script would work as follows:

mylength = 4
resultz = binary_seq_generator(mylength)
puts "#{resultz}"

#resultz, not necessarily in this order:

["0000","0001","0010","0011","0100","0101","0110","0111","1000","1001","1010","1011","1100","1101","1110","1111"]

Try this:

def binary_seq_generator(n)
(0...(1 << n)).map {|e| "%0#{n}d" % e.to_s(2) }
end

Doesn't necessarily roll off the fingers as readily as some Ruby
idioms do :slight_smile: But I think all or most of what you need is there, and
there are some interesting bits to it.

--
module Kernel
  alias_method :λ, :lambda
end

4

Robert Dober wrote:

···

On Sun, Aug 9, 2009 at 8:32 PM, David A. Black<dblack@rubypal.com> > wrote:

Try this:

def binary_seq_generator(n)
(0...(1 << n)).map {|e| "%0#{n}d" % e.to_s(2) }
end

Doesn't necessarily roll off the fingers as readily as some Ruby
idioms do :slight_smile: But I think all or most of what you need is there, and
there are some interesting bits to it.

Well 1.9 has to offer some elegance here

(1<<n).times.map{ | d | "%0{n}b" % d }

HTH
Robert

They worked! Thank you both very much - having a comprehensive
understanding of these operators will move my coding to the next level!
Very much appreciated, Tom
--
Posted via http://www.ruby-forum.com/\.

5

(1<<n).times.map{ | d | "%0{n}b" % d }

Oh I just forgot, maybe you need the "combinatoric" method :wink:

n.times.inject( [ "" ] ){ |s,| s.map{ |e| [ e + "0", e + "1" ] }.flatten }

6

Robert Dober wrote:

(1<<n).times.map{ | d | "%0{n}b" % d }

Perhaps safer to avoid the interpolation in the format string, using '*'
to give the number of digits.

"%0*b" % [8,123]

=> "01111011"

···

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

7

Hi --

···

On Mon, 10 Aug 2009, Robert Dober wrote:

On Sun, Aug 9, 2009 at 8:32 PM, David A. Black<dblack@rubypal.com> wrote:

Hi --

On Mon, 10 Aug 2009, Tom Best wrote:

I'm rather new to Ruby. I feel this should be very simple, but I'm
having trouble:

I'd like to write a script to work through all possible binary sequences
of length n.

The script would work as follows:

mylength = 4
resultz = binary_seq_generator(mylength)
puts "#{resultz}"

#resultz, not necessarily in this order:

["0000","0001","0010","0011","0100","0101","0110","0111","1000","1001","1010","1011","1100","1101","1110","1111"]

Try this:

def binary_seq_generator(n)
(0...(1 << n)).map {|e| "%0#{n}d" % e.to_s(2) }
end

Doesn't necessarily roll off the fingers as readily as some Ruby
idioms do :slight_smile: But I think all or most of what you need is there, and
there are some interesting bits to it.

Well 1.9 has to offer some elegance here

(1<<n).times.map{ | d | "%0{n}b" % d }

Good idea -- I was definitely doing an extra round trip to binary :slight_smile:

David

--
David A. Black / Ruby Power and Light, LLC / http://www.rubypal.com
Q: What's the best way to get a really solid knowledge of Ruby?
A: Come to our Ruby training in Edison, New Jersey, September 14-17!
    Instructors: David A. Black and Erik Kastner
    More info and registration: http://rubyurl.com/vmzN

8

Robert Dober wrote:

(1<<n).times.map{ | d | "%0{n}b" % d }

Perhaps safer to avoid the interpolation in the format string, using '*'
to give the number of digits.

"%0*b" % [8,123]

=> "01111011"

Well safer, you mean regarding to my typo, well spotted ;).
This is a fascinating idiom I was not aware of. I too prefer it, thx
for sharing.

Cheers
Robert

···

On Mon, Aug 10, 2009 at 10:43 AM, Brian Candler<b.candler@pobox.com> wrote:

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

--
module Kernel
  alias_method :λ, :lambda
end