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c#linqcollections

Check for any element that exists in two collections

I'm wondering if Linq has a method to check if two collections have at least a single element in common. I would expect something like this:

var listA = new List<int>() { some numbers };
var listB = new List<int>() { some numbers, potentially also in list A };

bool hasSameElements = listA.hasMatchingElements(listB);

Does it exists in Linq or should I write a custom method for it?

I am aware of the Intersect method, but doesn't this yield the entire intersection set? I'm only interested in checking IF the two collection intersect, yielding the entire set seems like a waste, especially on larger collections.

Solution

  • Sounds like you just want:

    bool hasSameElements = listA.Intersect(listB).Any();

    EDIT: As noted in comments, Intersect uses lazy evaluation. It defers all execution until the first element is read from the result; at that point it will load all of listB into a set, and then stream listA until it finds a result to yield. At that point, Any() will return true and so no more work will be done. See my Edulinq post on Intersect for more information.