c# - Select subset of elements by comparing them with each other in LINQ -

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i trying construct linq query take list of elements, , based on comparison between elements in list, select ones meet criteria. this:

var subset = set.somelinqquery((e1,e2) => e1 == e2);

subset contains e1 of set e1 == e2. ideas? thought of having nested loop, realized there must have been way in linq.

you need method generate unique pairs of items original set. here’s implementation of that:

/// <summary> /// returns enumeration of tuples containing unique pairs of distinct /// elements source collection. example, input sequence /// { 1, 2, 3 } yields pairs [1,2], [1,3] , [2,3] only. /// </summary> public static ienumerable<tuple<t, t>> uniquepairs<t>(this ienumerable<t> source) {     if (source == null)         throw new argumentnullexception("source");     return uniquepairsiterator(source); } private static ienumerable<tuple<t, t>> uniquepairsiterator<t>(ienumerable<t> source) {     // make sure 'source' evaluated once     ilist<t> arr = source ilist<t> ?? source.tolist();     (int = 0; < arr.count - 1; i++)         (int j = + 1; j < arr.count; j++)             yield return new tuple<t, t>(arr[i], arr[j]); }

now can achieve wanted:

var results = set.uniquepairs()                  .where(pair => pair.item1 == pair.item2)                  .select(pair => pair.item1);

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