Just to be an ass

MapReduce.cs

namespace OX.MapReduce
{
    using System;
    using System.Linq;
    using System.Threading.Tasks;

    public static class MapReduce
    {
        public static Task<T> Start<U, V, T>(Func<U, V> m, Func<V[], T> r, params U[] i) {
            return R(r, C(m, i));
        }

        static Task<T> R<V, T>(Func<V[], T> r, Task<V>[] m) {
            return Task.Factory.ContinueWhenAll(m, t => P(r, t));
        }

        static T P<V, T>(Func<V[], T> r, Task<V>[] t) {
            return r((from k in t select k.Result).ToArray());
        }

        static Task<V>[] C<U, V>(Func<U, V> m, U[] i) {
            var t = new Task<V>[i.Length];

            for (int j = 0; j < i.Length; ++j) t[j] = Task.Factory.StartNew(() => m(i[j]));

            return tasks;
        }
    }
}