Basically I'd like to make a Dictionary work with duplicate keys without going into custom comparer implementations. There is an idea of:
Dictionary<key, List<value>>
but it still has some overhead. I wish Dictionary had "AllowDuplicates".
views:
1330answers:
5
+3
A:
Not in the Fx < 3.5.. You can implement one, obviously, with a Dictionary of IList objects. But then you have the encapsulation issue/responsibility.
If you're using .NET 3.5, use the Lookup class.
Ryan Emerle
2009-02-16 00:21:19
A:
By definition, a Dictionary contains unique keys. Your example above is effectively a sort of two-dimensional keyed array, a structure I've used many times. Why would you want to have duplicate keys? If you did, how would the Dictionary uniquely address its members?
Dave Swersky
2009-02-16 00:22:00
Consider a real-world dictionary listing different meanings for the same word. Multiple entries with a common key. Nothing contradictory about that. Members could be addressed by a lookup returning a collection or Enumerable. C++ has had a multimap for ages. It's not an impossible problem. :)
jalf
2009-02-16 02:05:05
+2
A:
.NET 2.0: PowerCollections contains the OrderedMultiDictionary.
Mitch Wheat
2009-02-16 00:23:50
It's a pity that such a potentially useful class has a few limitations. Such as no public constructor or ability to add/remove items.
Ray
2009-02-16 00:40:45
@Ray, Agree completely. Although I guess that's why it's called Lookup rather than something like MultiDictionary, to hint that it's an immutable lookup of some sort rather than a collection to be manipulated. The OP's suggestion of a Dictionary<key, List<value>> would be much more flexible.
LukeH
2009-02-16 01:13:13
A:
“Why would you want to have duplicate keys? “
It is the sorted part of the collection I am lazy about.
I want to sort by things like voltage, amps or temp in my collection and return the interment identifier value i am storing for this sensor.
I'd like to iterate through the top most and lowest most values of these sensors and show the identifiers of some of the sensors I need to check out even if there happens to be some duplication. Use the index as a tiebreaker, or select one at random I don't care.
Alden
2010-05-20 08:16:12