Generate all possibles combinations of an array with a length within a given range

Question

How can I generate all possible combinations of elements of an array with a length within a given range? E.g.:

('a'..'f').to_a.all_possibilities(3, 5) 

should produce an array like:

['abc', 'abd', 'abe', 'abf', ..., 'abcde', 'abcdf', 'abcda', ...] 

including from "abc" (three characters) up to the last possible combination of ('a'..'f').to_a with five characters length. I have no idea how to do this. Any help?

Answer 1

Array#combination is stdlib:

[1] pry(main)> a = ('a'..'f').to_a => ["a", "b", "c", "d", "e", "f"] [2] pry(main)> a.combination(3).to_a => [["a", "b", "c"],  ["a", "b", "d"],  ["a", "b", "e"],  ["a", "b", "f"],  ["a", "c", "d"],  ["a", "c", "e"],  ["a", "c", "f"],  ["a", "d", "e"],  ["a", "d", "f"],  ["a", "e", "f"],  ["b", "c", "d"],  ["b", "c", "e"],  ["b", "c", "f"],  ["b", "d", "e"],  ["b", "d", "f"],  ["b", "e", "f"],  ["c", "d", "e"],  ["c", "d", "f"],  ["c", "e", "f"],  ["d", "e", "f"]] 

if you want all combinations of size min to max:

(min..max).flat_map{|size| a.combination(size).to_a } 

If you want them converted to strings, just replace .to_a with .map(&:join).