title: Is there a C# Data structure to map keys to multiple values?
body: <p>Is there a C# data structure to map keys to multiple values?  I have a collection of items that I want to key by name; however, the name is not unique.  Hashtable and Dictionary only allow unique keys.  Lookup seems close to what I want; however, it is not mutable.</p>
  
  <p>Is there a built in data structure that I'm missing or do I need to build one myself?</p>