title: Difference between Lookup() and Dictionary(Of list())
body: <p>I'm trying to wrap my head around which data structures are the most efficient and when / where to use which ones.</p>
  
  <p>Now, it could be that I simply just don't understand the structures well enough, but how is an <code>ILookup(of key, ...)</code> different from a <code>Dictionary(of key, list(of ...))</code>?</p>
  
  <p>Also where would I want to use an <code>ILookup</code> and where would it be more efficient in terms of program speed / memory / data accessing, etc?</p>