How to get duplicate items from a list using LINQ?

c# linq duplicates
Thorin Oakenshield picture Thorin Oakenshield · Sep 28, 2010 · Viewed 180.1k times · Source

I'm having a List<string> like:

List<String> list = new List<String>{"6","1","2","4","6","5","1"};

I need to get the duplicate items in the list into a new list. Now I'm using a nested for loop to do this.

The resulting list will contain {"6","1"}.

Is there any idea to do this using LINQ or lambda expressions?

Answer

Lee picture Lee · Sep 28, 2010 
var duplicates = lst.GroupBy(s => s)
    .SelectMany(grp => grp.Skip(1));

Note that this will return all duplicates, so if you only want to know which items are duplicated in the source list, you could apply Distinct to the resulting sequence or use the solution given by Mark Byers.

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