Best way to find out if IEnumerable<> has unique values

Question

I have a lot of code in which I do something like this

bool GetIsUnique(IEnumerable values)
{
    return values.Count() == values.Distinct().Count;
}
         


        

Answer 1

You would be doing two loops through the data for the above - once to get the count, once to get the distinct count. Especially bad if the first two items are identical! Try something like this:

bool GetIsUnique(IEnumerable values)
{
    HashSet hashSet = new HashSet();
    foreach(var value in values)
    {
        if (hashSet.Contains(value))
        {
            return false;
        }
        hashSet.Add(value);
    }
    return true;
}

This one will finish as soon as it finds a duplicate. Obviously it on the speed of the hash lookup but given Distinct uses a set internally I'd still expect it to be quicker.