Offer easy way to handle collections and combinations thereof

TDF already allows to perform some operations on collections in a transparent way, for example histogram filling. It would be nice to have a high level way to perform things like:

• coll<A> -> coll<B> where there is a method B A::GetAttr()
• coll<A>, coll<B> -> coll<C> via a function C f(A,B) in two cases: nested loop (N^2) and linear (N)

Languages like scala provide utilities to approach this issue: http://alvinalexander.com/scala/how-to-transform-collections-map-method-anonymous-functions-scala). Perhaps also looking at Python itertools can help.