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

Question

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 1

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.

Answer 2

You can use this extension method for enumerables containing more complex types:

IEnumerable<Foo> distinctList = sourceList.DistinctBy(x => x.FooName);  public static IEnumerable<TSource> DistinctBy<TSource, TKey>(     this IEnumerable<TSource> source,     Func<TSource, TKey> keySelector) {     var knownKeys = new HashSet<TKey>();     return source.Where(element => knownKeys.Add(keySelector(element))); }