Test if all values in a list are unique

Question

I have a small list of bytes and I want to test that they're all different values. For instance, I have this:

List<byte> theList = new List<byte> { 1,4,3,6,1 }; 

What's the best way to check if all values are distinct or not?

Answer 1

bool isUnique = theList.Distinct().Count() == theList.Count(); 

Answer 2

Here's another approach which is more efficient than Enumerable.Distinct + Enumerable.Count (all the more if the sequence is not a collection type). It uses a HashSet<T> which eliminates duplicates, is very efficient in lookups and has a count-property:

var distinctBytes = new HashSet<byte>(theList); bool allDifferent = distinctBytes.Count == theList.Count; 

or another - more subtle and efficient - approach:

var diffChecker = new HashSet<byte>(); bool allDifferent = theList.All(diffChecker.Add); 

HashSet<T>.Add returns false if the element could not be added since it was already in the HashSet. Enumerable.All stops on the first "false".