Gluip Gluip - 1 year ago 89
C# Question

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

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

bool GetIsUnique(IEnumerable<T> values)
return values.Count() == values.Distinct().Count;

Is there a better faster nicer way to do this?

Answer Source

Your method needs to iterate through the sequence twice, with a few of potential drawbacks:

  1. Iterating twice will be slower than iterating once for sequences of any significant size.
  2. Some sequences will throw an exception if you try to iterate them more than once; others might return different results for subsequent iterations.
  3. Your method uses Count which needs to iterate the entire sequence each time. There's no reason why you shouldn't break-out early as soon as you know that there's a duplicate value.

The following method only needs to iterate through the sequence once, and will break-out early as soon as any duplicate value is encountered:

bool GetIsUnique<T>(IEnumerable<T> values)
    var set = new HashSet<T>();

    foreach (T item in values)
        if (!set.Add(item))
            return false;
    return true;
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