Difference between Lookup() and Dictionary(Of list())

Question

I\'m trying to wrap my head around which data structures are the most efficient and when / where to use which ones.

Now, it could be that I simply just don\'t unders

Answer 1

Another difference not mentioned yet is that Lookup() supports null keys:

Lookup class implements the ILookup interface. Lookup is very similar to a dictionary except multiple values are allowed to map to the same key, and null keys are supported.