System\Linq\ParallelEnumerable.cs (3)
1345return GroupBy<TSource, TKey, TElement>(source, keySelector, elementSelector, null);
1501return source.GroupBy<TSource, TKey, TElement>(keySelector, elementSelector, comparer)
5233ParallelQuery<IGrouping<TKey, TElement>> groupings = source.GroupBy(keySelector, elementSelector, comparer);