Issue #4907 has been updated by mame (Yusuke Endoh).

Status changed from Open to Assigned
Assignee set to mrkn (Kenta Murata)


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Feature #4907: enumerable#permutation and combination
https://bugs.ruby-lang.org/issues/4907#change-25137

Author: neleai (Ondrej Bilka)
Status: Assigned
Priority: Normal
Assignee: mrkn (Kenta Murata)
Category: 
Target version: 


Hello
Methods permutation and combination are defined for array but it make more sense to define them for enumerable. 
Here is sample implementation which for simplicity works only with blocks.
Note that implementation works lazily. 
It changes traversal order but documentation states that order is unspecified.

module Enumerable
 def perm(n)
 comb(n){|ary|
 ary.permutation{|p| yield(p)}
 }
 end
 def comb(n,&m)
 ary=[]
 e=to_enum.with_index
 _comb(e,n-1,1.0/0.0,ary,m)
 end
def _comb(e,n,bound,ary,m)
    e.each{|el,i|
      return if i>=bound
      ary[n]=el
      if n==0
        m.call(ary)
      else
        _comb(e,n-1,i,ary,m)
      end
    }
  end

end
[1,2,4,3,5].comb(2){|a| puts a.inspect}
(1..4).comb(2){|a| puts a.inspect}
(1..4).perm(2){|a| puts a.inspect}



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