/// <summary>Applies a key-generating function to each element of the input stream and yields a stream of unique keys and their frequency.</summary>
/// <param name="projection">A function to transform items of the input stream into comparable keys.</param>
/// <param name="stream">The input stream.</param>
/// <returns>A stream of tuples where each tuple contains the unique key and a sequence of all the elements that match the key.</returns>
public static Stream<Tuple<TKey, int>> CountBy<TSource, TKey>(this Stream<TSource> stream, Func<TSource, TKey> projection)
{
return CSharpProxy.CountBy(stream, projection);
}
/// <summary>
/// Applies a key-generating function to each element of a CloudFlow and return a CloudFlow yielding unique keys and their number of occurrences in the original sequence.
/// </summary>
/// <param name="projection">A function that maps items from the input CloudFlow to keys.</param>
/// <param name="stream">The input CloudFlow.</param>
public static CloudFlow <Tuple <TKey, long> > CountBy <TSource, TKey>(this CloudFlow <TSource> stream, Func <TSource, TKey> projection)
{
return(CSharpProxy.CountBy(stream, projection));
}