itertools.groupby

[Steve Howell]

--- Raymond Hettinger <python at rcn.com> wrote:

> +  The operation of \function{groupby()} is similar
> to the \code{uniq}
> filter
> +  in \UNIX{}.  [...]

Thanks!

The comparison of groupby() to "uniq" really clicks
with me.  

To the extent that others like the Unix command line
analogy for understanding Python idioms, I compiled
the following list, which includes a couple groupby
examples from Raymond.


>>> 'abacadabra'[:5] # head -5
abaca

>>> 'abacadabra'[-5:] # tail -5
dabra

>>> [word for word in 'aaa,abc,foo,zzz,cba'.split(',')
if 'a' in word] # grep a
['aaa', 'abc', 'cba']

>>> sorted('abracadabra')   # sort
['a', 'a', 'a', 'a', 'a', 'b', 'b', 'c', 'd', 'r',
'r']

>>> list(reversed(sorted('abracadabra')))   # sort -r
['r', 'r', 'd', 'c', 'b', 'b', 'a', 'a', 'a', 'a',
'a']

>>> [k for k, g in groupby(sorted('abracadabra'))]   #
sort | uniq
['a', 'b', 'c', 'd', 'r']

>>> [(k, len(list(g))) for k, g in
groupby(sorted('abracadabra'))]   # sort | uniq -c
[('a', 5), ('b', 2), ('c', 1), ('d', 1), ('r', 2)]

>>> [k for k, g in groupby(sorted('abracadabra')) if
len(list(g)) > 1] # sort | uniq -d
['a', 'b', 'r']


       
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