[Numpy-discussion] Numpy 'groupby'

[Wes McKinney]

On Wed, Jan 11, 2012 at 7:05 AM, Neal Becker <ndbecker2 at gmail.com> wrote:
> Michael Hull wrote:
>
>> Hi Everyone,
>> First off, thanks for all your hard work on numpy, its a really great help!
>> I was wondering if there was a standard 'groupby' in numpy, that
>> similar to that in itertools.
>> I know its not hard to write with np.diff, but I have found myself
>> writing it on more than a couple of occasions, and wondered if
>>  there was a 'standarised' version I was missing out on??
>> Thanks,
>>
>>
>> Mike
>
> I've played with groupby in pandas.
>
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I agree (unsurprisingly) that pandas is your best bet:

http://pandas.sourceforge.net/groupby.html

I've had it on my TODO list to extend the pandas groupby engine (which
has grown fairly sophisticated) to work with generic ndarrays and
record arrays:

https://github.com/wesm/pandas/issues/123

It shouldn't actually be that hard for most simple cases. I could
imagine the results of a groupby being somewhat difficult to interpret
without axis labeling/indexing, though.

cheers,
Wes