/// <summary>
/// Groups the elements of a sequence according to a specified key selector function
/// and creates a result value from each group and its key.
/// </summary>
/// <typeparam name="TKey">The return-type of the transform used to group the sequence</typeparam>
/// <typeparam name="TResult">The final values to be yielded after processing</typeparam>
/// <typeparam name="TSource">The values to be yielded by the original data-source</typeparam>
/// <param name="comparer">Used to compare grouping keys</param>
/// <param name="keySelector">A function to extract the key for each element in hte original sequence.</param>
/// <param name="resultSelector">A function to create a result value from each group.</param>
/// <param name="source">The data-source to be grouped</param>
/// <remarks>This will force each unique grouping key to
/// be buffered, but not the data itself</remarks>
public static IDataProducer <TResult> GroupBy <TSource, TKey, TResult>
(this IDataProducer <TSource> source,
Func <TSource, TKey> keySelector,
Func <TKey, IDataProducer <TSource>, TResult> resultSelector,
IEqualityComparer <TKey> comparer)
{
return(source.GroupBy(keySelector,
elt => elt,
resultSelector,
comparer));
}
/// <summary>
/// Groups the elements of a sequence according to a specified key selector function
/// and creates a result value from each group and its key. The elements of each
/// group are projected by using a specified function.
/// </summary>
/// <typeparam name="TElement">The return-type of the transform used to process the
/// values within each grouping.</typeparam>
/// <typeparam name="TKey">The return-type of the transform used to group the sequence</typeparam>
/// <typeparam name="TSource">The values to be yielded by the original data-source</typeparam>
/// <param name="comparer">Used to compare grouping keys</param>
/// <param name="elementSelector">A function to map each source element to an element in the appropriate group</param>
/// <param name="keySelector">A function to extract the key for each element in hte original sequence.</param>
/// <param name="source">The data-source to be grouped</param>
/// <remarks>This will force each unique grouping key to
/// be buffered, but not the data itself</remarks>
public static IDataProducer <IProducerGrouping <TKey, TElement> > GroupBy <TSource, TKey, TElement>
(this IDataProducer <TSource> source,
Func <TSource, TKey> keySelector,
Func <TSource, TElement> elementSelector,
IEqualityComparer <TKey> comparer)
{
return(source.GroupBy(keySelector,
elementSelector,
(key, elements) => (IProducerGrouping <TKey, TElement>) new ProducerGrouping <TKey, TElement>(key, elements),
comparer));
}