public static IEnumerable <IGrouping <TKey, TSource> > GroupBy <TSource, TKey>(this IAdjacentGroupingSource <TSource> source, Func <TSource, TKey> keySelector, IEqualityComparer <TKey> comparer = null)
{
if (source == null)
{
throw new ArgumentNullException("source");
}
if (keySelector == null)
{
throw new ArgumentNullException("keySelector");
}
return(AdjacentGroupingEnumerable(source, keySelector, comparer));
}
private static IEnumerable <IGrouping <TKey, TSource> > AdjacentGroupingEnumerable <TSource, TKey>(IAdjacentGroupingSource <TSource> source, Func <TSource, TKey> keySelector, IEqualityComparer <TKey> comparer)
{
if (comparer == null)
{
comparer = EqualityComparer <TKey> .Default;
}
using (var en = source.GetEnumerator())
{
if (en.MoveNext())
{
var currentGroup = new Grouping <TKey, TSource>(keySelector(en.Current));
currentGroup.Elements.Add(en.Current);
while (en.MoveNext())
{
//Test whether current element starts a new group
TKey newKey = keySelector(en.Current);
if (!comparer.Equals(newKey, currentGroup.Key))
{
//Yield the previous group and start next one
yield return(currentGroup);
currentGroup = new Grouping <TKey, TSource>(newKey);
}
//Add element to the current group
currentGroup.Elements.Add(en.Current);
}
//Yield the last group of sequence
yield return(currentGroup);
}
}
}