groupby and itemgetter

Roman Bertle bertle at smoerz.org
Fri Oct 6 11:13:36 CEST 2006


Hello,

there is an example how to use groupby in the itertools documentation
(http://docs.python.org/lib/itertools-example.html):

# Show a dictionary sorted and grouped by value
>>> from operator import itemgetter
>>> d = dict(a=1, b=2, c=1, d=2, e=1, f=2, g=3)
>>> di = sorted(d.iteritems(), key=itemgetter(1))
>>> for k, g in groupby(di, key=itemgetter(1)):
...     print k, map(itemgetter(0), g)
...
1 ['a', 'c', 'e']
2 ['b', 'd', 'f']
3 ['g']

Now i wonder why itemgetter is used in this example. More
straightforward is:

>>> d = dict(a=1, b=2, c=1, d=2, e=1, f=2, g=3)
>>> di = sorted(d.iterkeys(), key=d.get)
>>> for k, g in groupby(di, key=d.get):
...     print k, list(g)
...
1 ['a', 'c', 'e']
2 ['b', 'd', 'f']
3 ['g']

This code does not need the operator module, and its also faster (tested
using timeit). Why was the, imho, more complicated version used as
example in the documentation?

Regards, Roman



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