How to use LINQ to find all combinations of n items from a set of numbers?

Question

I\'m trying to write an algorithm to select all combinations of n values from a set of numbers.

For instance, given the set: 1, 2, 3, 7, 8, 9

Al

Answer 1

Usage:

var results = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 }.DifferentCombinations(3);

Code:

public static class Ex
{
    public static IEnumerable> DifferentCombinations(this IEnumerable elements, int k)
    {
        return k == 0 ? new[] { new T[0] } :
          elements.SelectMany((e, i) =>
            elements.Skip(i + 1).DifferentCombinations(k - 1).Select(c => (new[] {e}).Concat(c)));
    }
}