Permutations of single array in expected array of arrays

Question

new_variant_permutations = all_value_arrays[1..].inject(all_value_arrays[0]) { |m, v| m.product(v).map { |perm| perm.flatten.sort } }

This line if given an all_value_arrays which is basically an array of arrays like [[1,2],[3,4]] returns possible permutations such as [[1,3],[1,4],[2,3],[2,4]] However if all_value_arrays is a single array inside an array like [[1,2,3,4]], instead of getting my expected [[1],[2],[3],[4]] I get [1,2,3,4] and this causes a problem with my code later on How can i avoid this happening and maintain the consistency of array of arrays as in my first example? TIA

Why do you expect the output [[1],[2],[3],[4]] with the input [[1,2,3,4]]? Are you trying to return all permutations of any length? — Ray Hamel
– Ray Hamel, Commented Apr 17, 2021 at 21:10
I'm trying to return permutations of my entry arrays that include one and exactly one value from the values in each of my entry arrays. — Omar Hussein
– Omar Hussein, Commented Apr 17, 2021 at 21:12
I have hotfixed by succeeding with new_variant_permutations = new_variant_permutations.map { |entry| entry.is_a?(Array) ? entry : [entry] } but I'd rather fix my initial code. — Omar Hussein
– Omar Hussein, Commented Apr 17, 2021 at 21:12
Whoops. Try .reduce(&:product).map { |perm| [perm].flatten } instead. — Ray Hamel
– Ray Hamel, Commented Apr 17, 2021 at 21:29

Omar Hussein · Accepted Answer · 2021-04-17 22:37:15Z

1

This one liner should do what you're asking for (return an array of arrays representing the cartesian product of the input arrays).

all_value_arrays.reduce(&:product).map { |perm| [perm].flatten }

edited Apr 17, 2021 at 22:37

Omar Hussein

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answered Apr 17, 2021 at 21:34

Ray Hamel

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Cary Swoveland · Accepted Answer · 2021-04-18 19:09:47Z

0

def doit(arr)
  arr.first.product(*arr.drop(1))
end

doit [[1,2],[3,4],[5,6]]
  #=> [[1, 3, 5], [1, 3, 6], [1, 4, 5], [1, 4, 6],
  #    [2, 3, 5], [2, 3, 6], [2, 4, 5], [2, 4, 6]]

doit [[1,2,3,4]]
  #=> [[1], [2], [3], [4]]

answered Apr 18, 2021 at 19:09

Cary Swoveland

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