Question

I need to remove multiple items from a Dictionary. A simple way to do that is as follows :

  List<string> keystoremove= new List<string>();   foreach (KeyValuePair<string,object> k in MyCollection)      if (k.Value.Member==foo)         keystoremove.Add(k.Key);   foreach (string s in keystoremove)         MyCollection.Remove(s); 

The reason why I can’t directly Remove the items in the foreach block is that this would throw an Exception ("Collection was modified…")

I’d like to do the following :

 MyCollection.RemoveAll(x =>x.Member==foo) 

But the Dictionary<> class doesn’t expose a RemoveAll(Predicate<> Match) method, like the List<> Class does.

What’s the best way (both performance wise and elegant wise) to do that?

Answer 1

Here’s an alternate way

foreach ( var s in MyCollection.Where(kv => kv.Value.Member == foo).ToList() ) {   MyCollection.Remove(s.Key); } 

Pushing the code into a list directly allows you to avoid the ‘removing while enumerating’ problem. The .ToList() will force the enumeration before the foreach really starts.