kj wrote:
>
>
>
>
>
> Task: given a list, produce a tally of all the distinct items in
> the list (for some suitable notion of "distinct").
>
> Example: if the list is ['a', 'b', 'c', 'a', 'b', 'c', 'a', 'b',
> 'c', 'a'], then the desired tally would look something like this:
>
> [('a', 4), ('b', 3), ('c', 3)]
>
> I find myself needing this simple operation so often that I wonder:
>
> 1. is there a standard name for it?
> 2. is there already a function to do it somewhere in the Python
> standard library?
>
> Granted, as long as the list consists only of items that can be
> used as dictionary keys (and Python's equality test for hashkeys
> agrees with the desired notion of "distinctness" for the tallying),
> then the following does the job passably well:
>
> def tally(c):
> t = dict()
> for x in c:
> t[x] = t.get(x, 0) + 1
> return sorted(t.items(), key=lambda x: (-x[1], x[0]))
>
> But, of course, if a standard library solution exists it would be
> preferable. Otherwise I either cut-and-paste the above every time
> I need it, or I create a module just for it. (I don't like either
> of these, though I suppose that the latter is much better than the
> former.)
>
> So anyway, I thought I'd ask. :)
Python 3.1 has, and 2.7 will have collections.Counter:
>>> from collections import Counter
>>> c = Counter("abcabcabca")
>>> c.most_common()
[('a', 4), ('c', 3), ('b', 3)]
Peter
--
http://mail.python.org/mailman/listinfo/python-list
