linq find duplicates and include based on condition c# code example

Example 1: c# linq check for duplicate

var duplicates = list.GroupBy(x => x.Key).Any(g => g.Count() > 1);

Example 2: c# find duplicates in list

var query = lst.GroupBy(x => x)
              .Where(g => g.Count() > 1)
              .Select(y => y.Key)
              .ToList();