CODEWITHSUNDEEP
.netcollectionsdictionaryintegerkey
Matthew
Matthew

Reputation: 10444

Alternative to Dictionary for Int32 keyed collections?

The hash of an Int32 is the value of the Int32 via:
Hashtables (Dictionary etc) with integer keys

As such, what value is added by using a Dictionary(Of Integer, someObject) (or any hashing collection, for that matter)?

I will, of course, need to use .Contains(integerKey) for either to prevent errors... but I can skip the hashing algorithm altogether, right?

What type would you use to optimize insertion/retrieval?

EDIT: I expect that I may perform on the order of 10^5 lookups and 10^3 insertions, and these operations are certainly not the bottleneck of my process.

Upvotes: 1

Views: 185

Answers (2)

Jon Skeet
Jon Skeet

Reputation: 1504022

Unless the numbers form a range 0...x (in which case you could just use a List<T> or even just an array) I would still go for the Dictionary<int, Whatever> approach. It's simple, it works, and it's almost certainly going to perform fast enough for you.

This really sounds like micro-optimization which ought to be skipped until you've proved that you've got a problem. How often are you going to be looking up items in the dictionary, compared with other operations?

EDIT: As Timwi says, there are indeed potential savings to be made here if this is really performance-critical. Without a generic key type and the virtual method calls to fetch hash codes and compare values, you could certainly do better. But I wouldn't trust any third-party collection as much as the built-in ones, and I certainly wouldn't trust my own collection implementations for anything non-trivial without a huge amount of testing... it would have to be a really significant bottleneck in the application as a whole before I considered moving away from the built-in types.

Upvotes: 4

Adam Houldsworth
Adam Houldsworth

Reputation: 64557

The Dictionary will just call GetHashCode on the type, so for Int32 I would imagine this to be pretty quick. Basically, I think it's already optimised enough for you.

What type I use depends on the type of the key to the value, I tend not to worry about performance in most uses.

Upvotes: 2

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