C# Dictionary ContainsValue look up by object attribute

Question

Hello,

I have Dictionary<long, Location> PostalCodes .

While i m adding new elements to this Dictionary I want to make a lookup to this dictionary and if the Location.PostalCode is not in this dictionary, I want to insert it. Otherwise I want to skip it. So , need to know if the PostalCode is already in the Collection. Cant use it as the key.

How to do this?

Thanks.

Answer 1

You can try:

if(PostalCodes.Values.All(l=>l.PostalCode != location.PostalCode))
{
    PostalCodes.Add(key /*what is it*/, location);
}

But this might get slow with large amount of data.

Answer 2

It sounds like you need another dictionary which does use it as the key - basically a bidirectional map. At least, that's if you want it to perform well. You could just look through every value in the map, but that would be an O(n) operation.

(Alternatively, if you're doing this once, just create a HashSet<Location> for all the locations you're using. You don't actually need the long, by the sounds of it for the purpose of the reverse lookup.)