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From: Paul Rubin <no.email@nospam.invalid>
Newsgroups: comp.lang.python
Subject: Re: Simple map/reduce utility function for data analysis
References: <967b61ce-5641-484a-bd76-5a09bd4247e0@w9g2000prg.googlegroups.com>
Date: Mon, 25 Apr 2011 19:42:17 -0700
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:4013

Raymond Hettinger <python@rcn.com> writes:
> Here's a handy utility function for you guys to play with:
>     http://code.activestate.com/recipes/577676/

Cute, but why not use collections.defaultdict for the return dict?
Untested:

   d = defaultdict(list)
   for key,value in ifilter(bool,imap(mapper, data)):
      d[key].append(value)
   ...