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Editorial Team
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Asked: 2026-06-14T22:37:32+00:00

I’m trying to write an Array extension that does something like this: I call

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I’m trying to write an Array extension that does something like this:

I call it like this:

%w[eggs bacon sausage].with_every_possibiity_of_multiples(2)

And it gives me these:

  [   
    %w[eggs, bacon, sausage],
    %w[eggs, eggs, bacon, sausage],
    %w[eggs, bacon, bacon, sausage],
    %w[eggs, bacon, sausage, sausage],
    %w[eggs, eggs, bacon, bacon, sausage],
    %w[eggs, eggs, bacon, bacon, sausage, sausage],
  ]

Hopefully it’s clear what’s going on here. If I had called it with an argument of 3 instead of 2, I’d have gotten an array of 9 elements, one of them being %w[eggs, eggs, eggs, bacon, sausage].

I’m struggling to come up with how to write this. Any suggestions?

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1 Answer

  1. Editorial Team

    As @sawa points out, you probably have your results mixed up. I’m guessing passing 2 gets you 8 elements, not 6, and passing 3 gets you 27, not 9.

    You can make good use of Array#repeated_combination to generate the number of times you want to repeat each element:

    class Array
  def with_every_possibility_of_multiples(n)
    (1..n).to_a.repeated_permutation(size).map do |repeats|
      zip(repeats).flat_map{|elem, nb| [elem] * nb}
    end
  end
end

food = %w[eggs bacon sausage]
food.with_every_possibility_of_multiples(2) # =>
[["eggs", "bacon", "sausage"], ["eggs", "bacon", "sausage", "sausage"], ["eggs", "bacon", "bacon", "sausage"],
 ["eggs", "bacon", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "sausage"],
 ["eggs", "eggs", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "sausage", "sausage"]]

food.with_every_possibility_of_multiples(3) # =>
[["eggs", "bacon", "sausage"],
 ["eggs", "bacon", "sausage", "sausage"],
 ["eggs", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "bacon", "bacon", "sausage"],
 ["eggs", "bacon", "bacon", "sausage", "sausage"],
 ["eggs", "bacon", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "bacon", "bacon", "bacon", "sausage"],
 ["eggs", "bacon", "bacon", "bacon", "sausage", "sausage"],
 ["eggs", "bacon", "bacon", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "sausage"],
 ["eggs", "eggs", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "bacon", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "bacon", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "bacon", "bacon", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "bacon", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "bacon", "bacon", "sausage", "sausage", "sausage"]]

    Note that repeated_permutation is new to Ruby 1.9.2. You can require 'backports' in earlier versions, or use an uglier version using product:

    # ...
(1..n).to_a.product(*[(1..n).to_a] * (size-1)).map do |repeats|
# ...
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