Flowdock
combination(p1) public

When invoked with a block, yields all combinations of length n of elements from ary and then returns ary itself. The implementation makes no guarantees about the order in which the combinations are yielded.

When invoked without a block, returns an enumerator object instead.

Examples:

    a = [1, 2, 3, 4]
    a.combination(1).to_a  #=> [[1],[2],[3],[4]]
    a.combination(2).to_a  #=> [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]
    a.combination(3).to_a  #=> [[1,2,3],[1,2,4],[1,3,4],[2,3,4]]
    a.combination(4).to_a  #=> [[1,2,3,4]]
    a.combination(0).to_a  #=> [[]] # one combination of length 0
    a.combination(5).to_a  #=> []   # no combinations of length 5
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