public static IOrderedEnumerable <TSource> OrderByDescending <TSource, TKey>(
this IEnumerable <TSource> source,
Func <TSource, TKey> keySelector,
IComparer <TKey> comparer)
{
if (source == null)
{
throw new ArgumentNullException("source");
}
if (keySelector == null)
{
throw new ArgumentNullException("keySelector");
}
comparer = new ReverseComparer <TKey>(comparer ?? Comparer <TKey> .Default);
return(new OrderedEnumerable <TSource, TKey>(source, keySelector, comparer));
}
public IOrderedEnumerable <TElement> CreateOrderedEnumerable <TKey>(Func <TElement, TKey> keySelector, IComparer <TKey> comparer, bool descending)
{
if (keySelector == null)
{
throw new ArgumentNullException("keySelector");
}
comparer = comparer ?? Comparer <TKey> .Default;
if (descending)
{
comparer = new ReverseComparer <TKey>(comparer);
}
// Copy to a local variable so we don't need to capture "this"
Func <TElement, TCompositeKey> primarySelector = compositeSelector;
Func <TElement, CompositeKey <TCompositeKey, TKey> > newKeySelector =
element => new CompositeKey <TCompositeKey, TKey>(primarySelector(element), keySelector(element));
IComparer <CompositeKey <TCompositeKey, TKey> > newKeyComparer =
new CompositeKey <TCompositeKey, TKey> .Comparer(compositeComparer, comparer);
return(new OrderedEnumerable <TElement, CompositeKey <TCompositeKey, TKey> >
(source, newKeySelector, newKeyComparer));
}