private static IEnumerable <T> DescendantsCore <T, K>(IEnumerable <T> source, Func <T, K> keySelector, Func <T, K> parentKeySelector, Equality <K> equality, K startKey, bool descendantsOnly = false, int?levelsCount = null)
where T : class
where K : class
{
PwrList <T> list = new PwrList <T>();
PwrFrameListView <T> view = new PwrFrameListView <T>(list);
int priorCount = list.Count;
if (descendantsOnly)
{
list.AddRange(source.Where(t => equality(parentKeySelector(t), startKey)));
}
else if (startKey != null)
{
list.AddRange(source.Where(t => equality(keySelector(t), startKey)));
}
int takeCount = list.Count - priorCount;
for (int passCount = 1; (!levelsCount.HasValue || levelsCount.Value > passCount) && takeCount > 0; passCount++)
{
view.FrameOffset = priorCount;
view.FrameSize = takeCount;
priorCount = list.Count;
list.AddRange(source.Where(t1 => parentKeySelector(t1) != null && view.Any(t2 => equality(keySelector(t2), parentKeySelector(t1)))));
takeCount = list.Count - priorCount;
}
return(list.AsEnumerable());
}
private static IEnumerable <T> AscendantsCore <T, K>(IEnumerable <T> source, Func <T, K> keySelector, Func <T, K> parentKeySelector, Equality <K> equality, K startKey, bool ascendantsOnly = false, int?levelsCount = null)
where T : class
where K : class
{
PwrList <T> list = new PwrList <T>();
T item = source.SingleOrDefault(t => equality(keySelector(t), startKey));
if (item != null && ascendantsOnly)
{
K parentKey = parentKeySelector(item);
item = parentKey != null?source.SingleOrDefault(t => equality(keySelector(t), parentKey)) : null;
}
if (item != null)
{
list.Add(item);
}
for (int passCount = 1; (!levelsCount.HasValue || levelsCount.Value > passCount) && item != null; passCount++)
{
K parentKey = parentKeySelector(item);
item = parentKey != null?source.SingleOrDefault(t => equality(keySelector(t), parentKey)) : null;
if (item != null)
{
list.Add(item);
}
}
return(list.AsEnumerable());
}