Problem with itertools.groupby.

[trebucket at gmail.com]

What am I doing wrong here?

>>> import operator
>>> import itertools
>>> vals = [(1, 11), (2, 12), (3, 13), (4, 14), (5, 15),
...      (1, 16), (2, 17), (3, 18), (4, 19), (5, 20)]
>>> for k, g in itertools.groupby(iter(vals), operator.itemgetter(0)):
...     print k, [i for i in g]
...
1 [(1, 11)]
2 [(2, 12)]
3 [(3, 13)]
4 [(4, 14)]
5 [(5, 15)]
1 [(1, 16)]
2 [(2, 17)]
3 [(3, 18)]
4 [(4, 19)]
5 [(5, 20)]

What I want is tuples starting with identical numbers to be grouped.  I
cannot figure out why this is not working.  If anyone has any insights,
I would appreciate it.

- Alex Ross