Documentation

Generate the combinations of \(k\) distinct objects chosen from the \(n\) elements of a list.

In how many ways can a committee of 3 be chosen from a group of 12 people? We all know that there are \({12 \choose 3} = 220\) possibilities, where \(n \choose k\) denotes the binomial coefficient. For pure mathematicians, this result may be great. But we want to really generate all the possibilities in a list.

Examples

>>> length $ combinations 3 [1..12]
220

>>> sort $ combinations 3 "abcdef"
["abc","abd","abe",...]