C# LINQ find duplicates in List

Question

Using LINQ, from a List, how can I retrieve a list that contains entries repeated more than once and their values?

Answer 1

Find out if an enumerable contains any duplicate :

var anyDuplicate = enumerable.GroupBy(x => x.Key).Any(g => g.Count() > 1);

Find out if all values in an enumerable are unique :

var allUnique = enumerable.GroupBy(x => x.Key).All(g => g.Count() == 1);