From: Robert Klemme <shortcutter@...>
Date: 2010-06-08T16:36:08+09:00
Subject: Re: array and hash combine methods

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

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


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