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Add support for unary plus and unary minus to collections.Counter()

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Raymond Hettinger 2011-08-09 13:00:40 -07:00
parent 18205baf25
commit fcb393c018
4 changed files with 31 additions and 1 deletions
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14
Doc/library/collections.rst
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@ -264,7 +264,7 @@ Common patterns for working with :class:`Counter` objects::
c.items() # convert to a list of (elem, cnt) pairs
Counter(dict(list_of_pairs)) # convert from a list of (elem, cnt) pairs
c.most_common()[:-n:-1] # n least common elements
c += Counter() # remove zero and negative counts
+c # remove zero and negative counts
Several mathematical operations are provided for combining :class:`Counter`
objects to produce multisets (counters that have counts greater than zero).
@ -284,6 +284,18 @@ counts, but the output will exclude results with counts of zero or less.
>>> c | d # union: max(c[x], d[x])
Counter({'a': 3, 'b': 2})
Unary addition and substraction are shortcuts for adding an empty counter
or subtracting from an empty counter.
>>> c = Counter(a=2, b=-4)
>>> +c
Counter({'a': 2})
>>> -c
Counter({'b': 4})
.. versionadded:: 3.3
Added support for unary plus and unary minus.
.. note::
Counters were primarily designed to work with positive integers to represent