Fastest way to Remove Duplicate Value from a list<> by lambda

c# list c#-4.0 lambda generic-list
Saeid picture Saeid · May 17, 2012 · Viewed 152.2k times · Source

what is fastest way to remove duplicate values from a list. Assume List<long> longs = new List<long> { 1, 2, 3, 4, 3, 2, 5 }; So I am interesting in use lambda to remove duplicate and returned : {1, 2, 3, 4, 5}. What is your suggestion?

Answer

Jon Skeet picture Jon Skeet · May 17, 2012

The easiest way to get a new list would be:

List<long> unique = longs.Distinct().ToList();

Is that good enough for you, or do you need to mutate the existing list? The latter is significantly more long-winded.

Note that Distinct() isn't guaranteed to preserve the original order, but in the current implementation it will - and that's the most natural implementation. See my Edulinq blog post about Distinct() for more information.

If you don't need it to be a List<long>, you could just keep it as:

IEnumerable<long> unique = longs.Distinct();

At this point it will go through the de-duping each time you iterate over unique though. Whether that's good or not will depend on your requirements.

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