From: "toy (Ivan Kuchin) via ruby-core" <ruby-core@...>
Date: 2025-09-07T19:00:20+00:00
Subject: [ruby-core:123184] [Ruby Feature#21564] Extend permutation, repeated_permutation, combination and repeated_combination argument

Issue #21564 has been reported by toy (Ivan Kuchin).

----------------------------------------
Feature #21564: Extend permutation, repeated_permutation, combination and repeated_combination argument
https://bugs.ruby-lang.org/issues/21564

* Author: toy (Ivan Kuchin)
* Status: Open
----------------------------------------
When using functions `permutation`, `repeated_permutation`, `combination` and `repeated_combination`, often one needs not one, but multiple permutation/combination sizes. Currently all functions accept one Integer argument (for `permutation` it is optional and defaults to array size), and it would be more powerful if it would accept also a range or a Enumerable:

```ruby
a = [1, 2, 3]

a.permutation(1..3).to_a # => [[1], [2], [3],
                         #     [1, 2], [1, 3], [2, 1], [2, 3], [3, 1], [3, 2],
                         #     [1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]

a.permutation([1, 3]).to_a # => [[1], [2], [3],
                           #     [1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]

a.permutation([3, 1]).to_a # => [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1],
                           #     [1], [2], [3]]

a.repeated_permutation([2, 1]).to_a # => [[1, 1], [1, 2], [1, 3], [2, 1], [2, 2], [2, 3], [3, 1], [3, 2], [3, 3],
                                    #     [1], [2], [3]]

a.combination(1..3).to_a # => [[1], [2], [3],
                         #     [1, 2], [1, 3], [2, 3],
                         #     [1, 2, 3]]

a.repeated_combination(1..3).to_a # => [[1], [2], [3],
                                  #     [1, 1], [1, 2], [1, 3], [2, 2], [2, 3], [3, 3],
                                  #     [1, 1, 1], [1, 1, 2], [1, 1, 3], [1, 2, 2], [1, 2, 3], [1, 3, 3], [2, 2, 2], [2, 2, 3], [2, 3, 3], [3, 3, 3]]
```

Ruby code to enhance current `permutation` would be:
```ruby
class Array
  alias_method :original_permutation, :permutation

  def permutation(counts, &block)
    return to_enum(__method__, counts) unless block

    if counts.is_a?(Enumerable)
      counts.each do |count|
        original_permutation(count, &block)
      end
    else
      original_permutation(counts, &block)
    end
  end
end
```



-- 
https://bugs.ruby-lang.org/
______________________________________________
 ruby-core mailing list -- ruby-core@ml.ruby-lang.org
 To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org
 ruby-core info -- https://ml.ruby-lang.org/mailman3/lists/ruby-core.ml.ruby-lang.org/