How do I iterate over items in a dict grouped by N number of elements?

Noah noah at noah.org
Fri Mar 14 02:34:49 CET 2008


What is the fastest way to select N items at a time from a dictionary?
I'm iterating over a dictionary of many thousands of items.
I want to operate on only 100 items at a time.
I want to avoid copying items using any sort of slicing.
Does itertools copy items?

This works, but is ugly:

>>> from itertools import *
>>> D = {'a':1, 'b':2, 'c':3, 'd':4, 'e':5, 'f':6, 'g':7, 'h':8, 'i':9, 'j':10}
>>> N = 3
>>> for G in izip(*[chain(D.items(), repeat(None, N-1))]*N):
...     print G
...
(('a', 1), ('c', 3), ('b', 2))
(('e', 5), ('d', 4), ('g', 7))
(('f', 6), ('i', 9), ('h', 8))
(('j', 10), None, None)

I'd prefer the last sequence not return None
elements and instead just return (('j',10)), but this isn't a huge
deal.

This works and is clear, but it makes copies of items:

>>> ii = D.items()
>>> for i in range (0, len(ii), N):
...     print ii[i:i+N]
...
[('a', 1), ('c', 3), ('b', 2)]
[('e', 5), ('d', 4), ('g', 7)]
[('f', 6), ('i', 9), ('h', 8)]
[('j', 10)]

--
Noah



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