Collection providing lookup by one of several keys

Question

What do you call a collection in which each item may be looked up by one of multiple keys? A partial, simplified definition in C# might be:

class MyDataStructure<TKey1, TKey2, TValue> {
    private List<TValue> _values;
    //map keys to indices
    private Dictionary<TKey1, int> _keys1;
    private Dictionary<TKey2, int> _keys2;

    public TValue GetByKey1(TKey1 key) ...
    public TValue GetByKey2(TKey2 key) ...
}

There's MultiKeyMap in Java, but that seems to lookup items based on a combination of keys, not by each key individually. Does what I've described have a well-established name?

EDIT

If there's not an established name, feel free to offer a new one. Or state your preference for one of these:

1. ChoiceKeyDictionary
2. AlternateKeyDictionary
3. DualKeyDictionary

Answer 1

I've heard the term "multi-key dictionary" used to describe this type of data structure.

Edit: Related questions have been asked on this topic:

http://stackoverflow.com/questions/1171812/multi-key-dictionary-in-c
http://stackoverflow.com/questions/1171913/multi-key-dictionaries-of-another-kind-in-c

Answer 2

They go by a few different names.

C# calls them Multi-Key Generic Dictionaries.

As a generic term, they're known as multimaps or (less specifically) multi-key associative arrays. Now, "associative array" is essentially a hash-table, so they can also be known as a multihash.

But if you're sticking with C# (as mentioned in the question), Multi-Key Dictionaries.

Keep in mind, if you are going with C#, if you are sure that each of your keys is unique among all the keys you can try this solution:

dict.add("key1", object)
dict.add("key2", object)