Create all combinations of n*m values

Question

Say I have a data structure of IEnumerable> like this:

{
    { A, B }
    { 1, 2, 3 }
    { Z }
}

Answer 1

private static IEnumerable> GetAllCombinations(IEnumerable> a)
    {
        if (!a.Skip(1).Any())
        {
            return a.First().Select(x => new[] { x });
        }

        var tail = GetAllCombinations(a.Skip(1)).ToArray();
        return a.First().SelectMany(f => tail.Select(x => new[] { f }.Concat(x)));
    }