Creates a sorted merge between an arbitrary amount of sorted sequences.

gistfile1.cs

public static IEnumerable<T> SortMerge<T, TKey>(Func<T, TKey> orderBy, params IEnumerable<T>[] sortedEnumerables)
{
    var enumerators = sortedEnumerables
        .Select(e => e.GetEnumerator())
        .Where(e => e.MoveNext())
        .ToList();

    while (enumerators.Any())
    {
        var next = enumerators
            .OrderBy(e => orderBy(e.Current))
            .First();
        var indexOfNext = enumerators.IndexOf(next);

        yield return enumerators[indexOfNext].Current;

        if (!enumerators[indexOfNext].MoveNext())
        {
            enumerators.RemoveAt(indexOfNext);
        }
    }
}