Hi, Thanks for the response! (See below for more discussion)
On Oct 23, 10:39 am, Raymond Hettinger <[EMAIL PROTECTED]> wrote: > [Duane] > > > LoTuples1 = [(1,1,0),(1,2,1),(1,3,3)] > > Set1=set(LoTuples1) > > LoTuples2 = [(2,1,3),(2,2,4),(2,3,2)] > > Set2=set(LoTuples2) > > > What I would like to be able to do is: > > > Set3 = Set1union(Set2) > > Set3.intersection(Set2, <use object[2]>) > > > to return: > > set([(2,1,3), (1,3,3)]) > > > How can one do this operation? > > Conceptually, there is more than one operation going on. First, > finding the attributes shared in both sets: > ca = set(t[2] for t in LoTuples1) & set(t[2] for t in LoTuples2) > which gives: > set([3]) In my use case, I already know object[2] is the key I wish to use, so I could do this without the first step. I am thinking of object[n] as the 'key' I wish to operate on, and the other items in the tuple are useful attributes I'll need in the end. > > Second, find any tuple which has that attribute (including multiple > results for the same attribute): > set(t for t in (LoTuples1 + LoTuples2) if t[2] in ca) > which returns: > set([(2, 1, 3), (1, 3, 3)]) > > Wanting multiple results for the same attribute value (i.e. both > (2,1,3) and (1,3,3) have 3 in the second position) is why multiple > steps are needed; otherwise, the behavior of intersection() is to > return a single representative of the equivalence class. > This second operation is really much like what I cam up with before I started looking into exploiting the power of sets (this same operation can be done strictly with lists, right?) Since what I _really_ wanted from this was the intersection of the objects (based on attribute 2), I was looking for a set-based solution, kinda like a decorate - <set operation> - undecorate pattern. Perhaps the problem does not fall into that category. Thanks for your help, Duane -- http://mail.python.org/mailman/listinfo/python-list
