C# - Removing Items from Dictionary in while loop

Question

I have this and all seems to work fine but not sure why and if its valid.

        Dictionary<string, List<string>> test = new Dictionary<string, List<string>>();

        while (test.Count > 0)
        {
            var obj = test.Last();
            MyMethod(obj);
            test.Remove(obj.Key);
        }

Update: Thanks for the answers, I have updated my code to explain why I don't do Dictionary.Clear();

Answer 1

I don't understand why you are trying to process all Dictonary entries in reverse order - but your code is OK.

It might be a bit faster to get a list of all Keys and process the entries by key instead of counting again and again...

E.G.:

var keys = test.Keys.OrderByDescending(o => o).ToList();

foreach (var key in keys)
{
    var obj = test[key];
    MyMethod(obj);
    test.Remove(key);
}

Dictonarys are fast when they are accessed by their key value. Last() is slower and counting is not necessary - you can get a list of all (unique) keys.