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Diffstat (limited to 'Doc')
| -rw-r--r-- | Doc/library/collections.rst | 36 |
1 files changed, 17 insertions, 19 deletions
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst index 13a92c4..fc2b802 100644 --- a/Doc/library/collections.rst +++ b/Doc/library/collections.rst @@ -188,26 +188,24 @@ For example:: >>> c = Counter() # a new, empty counter >>> c = Counter('gallahad') # a new counter from an iterable - >>> c = Counter({'a': 4, 'b': 2}) # a new counter from a mapping + >>> c = Counter({'red': 4, 'blue': 2}) # a new counter from a mapping The returned object has a dictionary style interface except that it returns a zero count for missing items (instead of raising a :exc:`KeyError` like a dictionary would):: - >>> c = Counter(['if', 'your', 'peril', 'be']) - >>> c['questions'] # count of a missing element is zero + >>> c = Counter(['egg', 'ham']) + >>> c['bacon'] # count of a missing element is zero 0 Assigning a count of zero or reducing the count to zero leaves the element in the dictionary. Use ``del`` to remove the entry entirely: >>> c = Counter(['arthur', 'gwain']) - >>> c['arthur'] = 0 # set the count of "arthur" to zero - >>> 'arthur' in c # but "arthur" is still in the counter + >>> c['arthur'] = 0 # set the count of 'arthur' to zero + >>> 'arthur' in c # but 'arthur' is still in the counter True >>> del c['arthur'] # del will completely remove the entry - >>> 'arthur' in c - False .. versionadded:: 2.7 @@ -267,25 +265,25 @@ Common patterns for working with :class:`Counter` objects:: dict(c) # convert to a regular dictionary 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:] # n least common elements + c.most_common()[:-n:-1] # n least common elements **References**: - * Wikipedia entry for `Multisets <http://en.wikipedia.org/wiki/Multiset>`_ +* Wikipedia entry for `Multisets <http://en.wikipedia.org/wiki/Multiset>`_ - * `Bag class <http://www.gnu.org/software/smalltalk/manual-base/html_node/Bag.html>`_ - in Smalltalk +* `Bag class <http://www.gnu.org/software/smalltalk/manual-base/html_node/Bag.html>`_ + in Smalltalk +* `C++ multisets <http://www.demo2s.com/Tutorial/Cpp/0380__set-multiset/Catalog0380__set-multiset.htm>`_ + tutorial with standalone examples - * `C++ multisets <http://www.demo2s.com/Tutorial/Cpp/0380__set-multiset/Catalog0380__set-multiset.htm>`_ - tutorial with standalone examples +* An early Python `Bag <http://code.activestate.com/recipes/259174/>`_ recipe + for Python 2.4 and a `Counter <http://code.activestate.com/recipes/576611/>`_ + comformant recipe for Python 2.5 and later - * An early Python `Bag <http://code.activestate.com/recipes/259174/>`_ recipe - for Python 2.4 and a `Counter <http://code.activestate.com/recipes/576611/>`_ - comformant recipe for Python 2.5 and later +* Use cases for multisets and mathematical operations on multisets. + Knuth, Donald. The Art of Computer Programming Volume II, + Section 4.6.3, Exercise 19 - * Use cases for multisets and mathematical operations on multisets. - Knuth, Donald. The Art of Computer Programming Volume II, - Section 4.6.3, Exercise 19 .. _deque-objects: |