Question

I have a List<string> which has some words duplicated. I need to find all words which are duplicates.

Any trick to get them all?

Answer 1

In .NET framework 3.5 and above you can use Enumerable.GroupBy which returns an enumerable of enumerables of duplicate keys, and then filter out any of the enumerables that have a Count of <=1, then select their keys to get back down to a single enumerable:

var duplicateKeys = list.GroupBy(x => x)
                        .Where(group => group.Count() > 1)
                        .Select(group => group.Key);