c# Dictionary: making the Key case-insensitive through declarations

Question

I have a Dictionary<string, object> dictionary. It used to be Dictionary<Guid, object> but other 'identifiers' have come into play and the Keys are now handled as strings.

The issue is that the Guid keys from my source data are coming as VarChar, so now a key of "923D81A0-7B71-438d-8160-A524EA7EFA5E" is not the same as "923d81a0-7b71-438d-8160-a524ea7efa5e" (wasn't a problem when using Guids).

What's really nice (and sweet) about the .NET framework is that I can do this:

Dictionary<string, CustomClass> _recordSet = new Dictionary<string, CustomClass>(
    StringComparer.InvariantCultureIgnoreCase);

And that works great. But what about a nested Dictionary? Like the following:

Dictionary<int, Dictionary<string, CustomClass>> _customRecordSet 
    = new  Dictionary<int, Dictionary<string, CustomClass>>();

How would I specify the string comparer on a nested dictionary like this?

Answer 1

When you add an element to the outer dictionary, you'll likely create a new instance of the nested dictionary, add it at this point, making use of the overloaded constructor that takes an IEqualityComparer<TKey>.

_customRecordSet.Add(0, new Dictionary<string, CustomClass>(StringComparer.InvariantCultureIgnoreCase));

---

Update 08/03/2017: Anecdotally, I read somewhere (I think in "Writing High-Performance .NET Code") that StringComparer.OrdinalIgnoreCase is more efficient when simply wanting to disregard the case of characters. This, however, is entirely unfounded by myself so YMMV.

Answer 2

You are going to have to initialize the nested dictionaries in order to use them. Just use the code you have above at that point.

Basically, you should have some code like this:

public void insert(int int_key, string guid, CustomClass obj)
{
    if (_customRecordSet.ContainsKey(int_key)
         _customRecordSet[int_key][guid] = obj;
    else
    {
         _customRecordSet[int_key] = new Dictionary<string, CustomClass> 
                                     (StringComparer.InvariantCultureIgnoreCase);
         _customRecordSet[int_key][guid] = obj;
    }
}