Creating permutations from a multi-dimensional array in Ruby

Question

I have the following multi-dimensional array in Ruby:

[[1,2], [3], [4,5,6]]

I need to have the following output:

[[1,3,4], [1,3,5], [1,3,6], [2,3,4], [2,3,5], [2,3,6]]

I have tried creating a recursive function, but I'm not having much luck.

Are there any Ruby functions that would help with this? Or is the only option to do it recursively?

Thanks

You should always show the code you've tried, even when it didn't work. Sometimes the fix is a minor tweak. Other times you'll get alternate solutions. Always, we'll be able to tell whether you've actually tried something or are just fishing for answers. — the Tin Man
– the Tin Man, Commented Apr 7, 2011 at 14:21

Mladen Jablanović · Accepted Answer · 2011-04-07 14:37:55Z

34

Yup, Array#product does just that (Cartesian product):

a = [[1,2], [3], [4,5,6]]
head, *rest = a # head = [1,2], rest = [[3], [4,5,6]]
head.product(*rest)
#=> [[1, 3, 4], [1, 3, 5], [1, 3, 6], [2, 3, 4], [2, 3, 5], [2, 3, 6]]

Another variant:

a.inject(&:product).map(&:flatten)
#=> [[1, 3, 4], [1, 3, 5], [1, 3, 6], [2, 3, 4], [2, 3, 5], [2, 3, 6]]

edited Apr 7, 2011 at 14:37

answered Apr 7, 2011 at 14:18

Mladen Jablanović

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