Array and hash combine methods

ruby-talk
1

Just thought I'd post a solution I came up with to finding
combinations (as in, permutations and combinations) of arrays. For
example, combining:

[1,2] and [3,4,5]

should return:

[[1,3],[1,4],[1,5],[2,3],[2,4],[2,5]]

which is easy enough. But I wanted something that combine several
arrays at once, ie:

[[1,2],[3,4,5],[6,7]].combine
=> [[1, 3, 6], [1, 3, 7], [1, 4, 6], [1, 4, 7], [1, 5, 6], [1, 5, 7],
[2, 3, 6], [2, 3, 7], [2, 4, 6], [2, 4, 7], [2, 5, 6], [2, 5, 7]]

I had a look around and couldn't find anything that worked for more
than two arrays, so I wrote my own:

class Array
  #expects self to be an array of arrays, returns all the combinations possible
  def combine
    #checks
    output_length = 1
    periods = []
    reverse.each { |sub_arr|
      periods << output_length
      raise "combine needs an array of arrays!" if !sub_arr.is_a? Array
      raise "combine is meaningless unless all the sub_arrays have at
least one element!" if sub_arr.length == 0
      output_length *= sub_arr.length
    }
    periods.reverse!
    output = (1..output_length).map { Array.new(length) }
    output.each_index { |i|
      periods.each_index { |j|
        output[i][j] = self[j][(i/periods[j])%self[j].length]
      }
    }
    output
  end
end

And the corresponding hash method:

class Hash
  #expects a hash eg. {a=>[1,2], b=>[3,4]}
  #returns an array eg. [{a=>1,b=>3}, {a=>1,b=4}, {a=>2,b=>3}, {a=>2,b=4}]
  def combine
    values.combine.map { |comb|
      Hash[*keys.zip(comb).inject([]) { |arr,e| arr + e }]
    }
  end
end

I'd love to hear other solutions to this problem - and where I should
have looked to find them... Oh and if anyone has suggestions for a
better name than 'combine', that'd be great.

Cheers,
-glen.

2

There is a Enumerable.combinations method in ruby facets which works like
this. Take a look at :

http://facets.rubyforge.org/api/core/classes/Enumerable.html#M000555

···

Le jeudi 14 décembre 2006 02:22, glen a écrit :

Just thought I'd post a solution I came up with to finding
combinations (as in, permutations and combinations) of arrays. For
example, combining:

[1,2] and [3,4,5]

should return:

[[1,3],[1,4],[1,5],[2,3],[2,4],[2,5]]

which is easy enough. But I wanted something that combine several
arrays at once, ie:

[[1,2],[3,4,5],[6,7]].combine
=> [[1, 3, 6], [1, 3, 7], [1, 4, 6], [1, 4, 7], [1, 5, 6], [1, 5, 7],
[2, 3, 6], [2, 3, 7], [2, 4, 6], [2, 4, 7], [2, 5, 6], [2, 5, 7]]

--
Olivier

3

glen wrote:

Just thought I'd post a solution I came up with to finding
combinations (as in, permutations and combinations) of arrays. For
example, combining:

[1,2] and [3,4,5]

should return:

[[1,3],[1,4],[1,5],[2,3],[2,4],[2,5]]

which is easy enough. But I wanted something that combine several
arrays at once, ie:

[[1,2],[3,4,5],[6,7]].combine
=> [[1, 3, 6], [1, 3, 7], [1, 4, 6], [1, 4, 7], [1, 5, 6], [1, 5, 7],
[2, 3, 6], [2, 3, 7], [2, 4, 6], [2, 4, 7], [2, 5, 6], [2, 5, 7]]

And why not something like:

  [1,2].combine([3,4]).combine([5,6,7])

I do that with this code:

class Array
  def combine(otherArray)
    aux =
    self.each do |self_elem|
      otherArray.each do |other_elem|
        aux << [self_elem,other_elem]
      end
    end
    aux.map {|elem| elem.flatten }
  end
end

Juan Matias

···

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

4

Juan, it would appear that glen posted this question/tip 3.5 years
ago. Any reason you were responding to it now? (Which, in turn, lured
me into responding. :slight_smile:

···

On Jun 7, 9:52 pm, Juan Matias <jmrepe...@gmail.com> wrote:

glen wrote:
> Just thought I'd post a solution I came up with to finding
> combinations (as in, permutations and combinations) of arrays. For
> example, combining:

5

I'd rather do this:

module Enumerable
  def combine(enum)
    if block_given?
      each do |*a|
        enum.each do |*b|
          yield *a, *b
        end
      end
      self
    else
      enum_for(:combine, enum)
    end
  end
end

[1,2].combine([3,4]) do |*a|
  p a
end

puts "--------------"

[1,2].combine([3,4]).each do |*a|
  p a
end

puts "--------------"

[1,2].combine([3,4]).combine([5,6]) do |*a|
  p a
end

puts "--------------"

[1,2].combine([3,4]).combine([5,6]).each do |*a|
  p a
end

Kind regards

robert

···

2010/6/8 Juan Matias <jmrepetti@gmail.com>:

glen wrote:

Just thought I'd post a solution I came up with to finding
combinations (as in, permutations and combinations) of arrays. For
example, combining:

[1,2] and [3,4,5]

should return:

[[1,3],[1,4],[1,5],[2,3],[2,4],[2,5]]

which is easy enough. But I wanted something that combine several
arrays at once, ie:

[[1,2],[3,4,5],[6,7]].combine
=> [[1, 3, 6], [1, 3, 7], [1, 4, 6], [1, 4, 7], [1, 5, 6], [1, 5, 7],
[2, 3, 6], [2, 3, 7], [2, 4, 6], [2, 4, 7], [2, 5, 6], [2, 5, 7]]

And why not something like:

[1,2].combine([3,4]).combine([5,6,7])

I do that with this code:

class Array
def combine(otherArray)
aux =
self.each do |self_elem|
otherArray.each do |other_elem|
aux << [self_elem,other_elem]
end
end
aux.map {|elem| elem.flatten }
end
end

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

6

Gavin Kistner wrote:

···

On Jun 7, 9:52�pm, Juan Matias <jmrepe...@gmail.com> wrote:

glen wrote:
> Just thought I'd post a solution I came up with to finding
> combinations (as in, permutations and combinations) of arrays. For
> example, combining:

Juan, it would appear that glen posted this question/tip 3.5 years
ago. Any reason you were responding to it now? (Which, in turn, lured
me into responding. :slight_smile:

Sure Gavin, I'm looking for something like that and found this post.
Maybe result useful to someone. You have another solution for this?
Thanks
--
Posted via http://www.ruby-forum.com/\.

7

Robert Klemme wrote:

�[1,2].combine([3,4]).combine([5,6,7])
� �end
� �aux.map {|elem| elem.flatten }
�end
end

I'd rather do this:

module Enumerable
  def combine(enum)
    if block_given?
      each do |*a|
        enum.each do |*b|
          yield *a, *b
        end
      end
      self
    else
      enum_for(:combine, enum)
    end
  end
end

[1,2].combine([3,4]) do |*a|
  p a
end

puts "--------------"

[1,2].combine([3,4]).each do |*a|
  p a
end

puts "--------------"

[1,2].combine([3,4]).combine([5,6]) do |*a|
  p a
end

puts "--------------"

[1,2].combine([3,4]).combine([5,6]).each do |*a|
  p a
end

Kind regards

robert

Great, I'll probe it,also I add a fix to my code:

class Array
  def combine(otherArray)
    aux =
    return otherArray if self.empty? #this line
    self.each do |self_elem|
      otherArray.each do |other_elem|
        aux << [self_elem,other_elem]
      end
    end
    aux.map {|elem| elem.flatten }
  end
end

Juan Matias

···

2010/6/8 Juan Matias <jmrepetti@gmail.com>:

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

8

The examples seem to be missing
If there is code snippets, it would help.
-Kamal.

···

________________________________
From: Juan Matias <jmrepetti@gmail.com>
To: ruby-talk ML <ruby-talk@ruby-lang.org>
Sent: Tue, June 8, 2010 12:33:24 AM
Subject: Re: array and hash combine methods

Gavin Kistner wrote:

On Jun 7, 9:52�pm, Juan Matias <jmrepe...@gmail.com> wrote:

glen wrote:
> Just thought I'd post a solution I came up with to finding
> combinations (as in, permutations and combinations) of arrays. For
> example, combining:

Juan, it would appear that glen posted this question/tip 3.5 years
ago. Any reason you were responding to it now? (Which, in turn, lured
me into responding. :slight_smile:

Sure Gavin, I'm looking for something like that and found this post.
Maybe result useful to someone. You have another solution for this?
Thanks
--
Posted via http://www.ruby-forum.com/\.