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Faster groupby! #179

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merged 6 commits into from
May 18, 2014
Merged

Faster groupby! #179

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623c448
Faster groupby!
eriknw May 10, 2014
76054c8
Add useful code comments to groupby including pythonic implementation
eriknw May 10, 2014
8365b4d
Small tweak to `groupby` to improve it for "real-world" data
eriknw May 10, 2014
6d33033
Add a new implementation of `groupby` that uses two dicts.
eriknw May 12, 2014
d871c94
No need to import `compatibility.iteritems` in `itertoolz`
eriknw May 12, 2014
42dc568
Choose a version of `groupby` that is easier to understand.
eriknw May 15, 2014
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18 changes: 13 additions & 5 deletions toolz/itertoolz.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,8 @@
import collections
import operator
from functools import partial
from toolz.compatibility import map, filter, filterfalse, zip, zip_longest
from toolz.compatibility import (map, filter, filterfalse, zip, zip_longest,
iteritems)


__all__ = ('remove', 'accumulate', 'groupby', 'merge_sorted', 'interleave',
Expand Down Expand Up @@ -66,12 +67,19 @@ def groupby(func, seq):
{False: [1, 3, 5, 7], True: [2, 4, 6, 8]}

See Also:
``countby``
countby
"""
d = collections.defaultdict(list)
d = {}
for item in seq:
d[func(item)].append(item)
return dict(d)
key = func(item)
if key not in d:
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Using try-except here might be a bit faster in cases with more than a few repeats. I get only modest improvements on my tiny benchmark though.

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The groupby_alt that I posted in the above always performs better than using a try-except here. You should really test groupby_alt too!

I get only modest improvements on my tiny benchmark though.

Yeah, the improvements can indeed be modest, but they are most significant when many items are the same. Also, the new implementation is always better than the old implementation for my benchmarks, including all the same, all different, and tiny seq.

d[key] = [item].append
else:
d[key](item)
# This is okay to do, because we are not adding or removing keys
for k, v in iteritems(d):
d[k] = v.__self__
return d


def merge_sorted(*seqs, **kwargs):
Expand Down