How to get all subsets of an array?

Question

Given an array: [dog, cat, mouse]

what is the most elegant way to create:

[,,]
[,,mouse]
[,cat,]
[,cat,mouse]
[dog,,]
[dog,,mouse]
[dog,         


        

Answer 1

Here is a variant of mqp's answer, that uses as state a BigInteger instead of an int, to avoid overflow for collections containing more than 30 elements:

using System.Numerics;

public static IEnumerable> GetSubsets(IList source)
{
    BigInteger combinations = BigInteger.One << source.Count;
    for (BigInteger i = 0; i < combinations; i++)
    {
        yield return Enumerable.Range(0, source.Count)
            .Select(j => (i & (BigInteger.One << j)) != 0 ? source[j] : default);
    }
}