On Apr 30, 3:48 am, James Stroud <[EMAIL PROTECTED]> wrote: > Prateek wrote: > > I have 3 variable length lists of sets. I need to find the common > > elements in each list (across sets) really really quickly. > > > Here is some sample code: > > > # Doesn't make sense to union the sets - we're going to do > > intersections later anyway > > l1 = reduce(operator.add, list(x) for x in l1) > > l2 = reduce(operator.add, list(x) for x in l2) > > l3 = reduce(operator.add, list(x) for x in l3) > > > # Should I do this in two steps? Maybe by intersecting the two > > shortest lists first? > > s = frozenset(l1) & frozenset(l2) & frozenset(l3) > > > I'm assuming frozensets are (somehow) quicker than sets because > > they're immutable. > > > Any code suggestions? Maybe using something in the new fancy-schmancy > > itertools module? > > > Thanks, > > Prateek > > I don't understand why you cast to list. I would propose: >
The reason why I'm casting to a list first is because I found that creating a long list which I convert to a set in a single operation is faster (although probably less memory efficient - which I can deal with) than doing all the unions. Prateek -- http://mail.python.org/mailman/listinfo/python-list
