From: Robert Klemme <shortcutter@...>
Date: 2010-09-15T17:42:42+09:00
Subject: Re: Iterate over a cartesian product.

2010/9/14 Jörg W Mittag <JoergWMittag+Ruby@googlemail.com>:
> Handy Gandy wrote:
>> I have an array of N arrays A_i: [A_1,A_2,...,A_N].
>>
>> I want to iterate over the cartesian product A_1xA_2...xA_N.
>>
>> Is there a simple way of doing this without specifying N?
>
>    ary = [[1, 2], [3, 4, 5], [6, 7, 8, 9]]
>    ary.first.product(*ary.drop(1))
>    # => [
>    # =>   [1, 3, 6], [1, 3, 7], [1, 3, 8], [1, 3, 9],
>    # =>   [1, 4, 6], [1, 4, 7], [1, 4, 8], [1, 4, 9],
>    # =>   [1, 5, 6], [1, 5, 7], [1, 5, 8], [1, 5, 9],
>    # =>   [2, 3, 6], [2, 3, 7], [2, 3, 8], [2, 3, 9],
>    # =>   [2, 4, 6], [2, 4, 7], [2, 4, 8], [2, 4, 9],
>    # =>   [2, 5, 6], [2, 5, 7], [2, 5, 8], [2, 5, 9]
>    # => ]

This looks nice.  How did you do the formatting?

If destruction is allowed, we can do:

irb(main):013:0> ary = [[1, 2], [3, 4, 5], [6, 7, 8, 9]]
=> [[1, 2], [3, 4, 5], [6, 7, 8, 9]]
irb(main):014:0> pp ary.shift.product(*ary)
[[1, 3, 6],
 [1, 3, 7],
 [1, 3, 8],
 [1, 3, 9],
 [1, 4, 6],
 [1, 4, 7],
 [1, 4, 8],
 [1, 4, 9],
 [1, 5, 6],
 [1, 5, 7],
 [1, 5, 8],
 [1, 5, 9],
 [2, 3, 6],
 [2, 3, 7],
 [2, 3, 8],
 [2, 3, 9],
 [2, 4, 6],
 [2, 4, 7],
 [2, 4, 8],
 [2, 4, 9],
 [2, 5, 6],
 [2, 5, 7],
 [2, 5, 8],
 [2, 5, 9]]
=> nil

Kind regards

robert

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