On 14/06/2006 8:06 AM, Gary Herron wrote: > John Machin wrote: >> On 13/06/2006 6:28 PM, Paul McGuire wrote: >> >> >>> (Oh, and I like groupby too! Combine it with sort to quickly create >>> histograms.) >>> >>> # tally a histogram of a list of values from 1-10 >>> dataValueRange = range(1,11) >>> data = [random.choice(dataValueRange) for i in xrange(10000)] >>> >>> hist = [ (k,len(list(g))) for k,g in itertools.groupby(sorted(data)) ] >>> >> That len(list(g)) looks like it uses O(N) memory just to find out what N >> is :-( >> > Not at all! A python list *knows* its length at all times. len() is a > constant time lookup of an internal attribute.
Did you see any reference to time in what I wrote? Did you notice the word "memory" at all? My point is that "g" is an iterator, and list(g) actually builds a list of size N, merely in order to use len(that_list) to count the number of items that g will produce. -- http://mail.python.org/mailman/listinfo/python-list
