How to sort Counter by value? - python

Use the Counter.most_common() method, it'll sort the items for you:

>>> from collections import Counter>>> x = Counter({'a':5, 'b':3, 'c':7})>>> x.most_common()[('c', 7), ('a', 5), ('b', 3)]

It'll do so in the most efficient manner possible; if you ask for a Top N instead of all values, a heapq is used instead of a straight sort:

>>> x.most_common(1)[('c', 7)]

Outside of counters, sorting can always be adjusted based on a key function; .sort() and sorted() both take callable that lets you specify a value on which to sort the input sequence; sorted(x, key=x.get, reverse=True) would give you the same sorting as x.most_common(), but only return the keys, for example:

>>> sorted(x, key=x.get, reverse=True)['c', 'a', 'b']

or you can sort on only the value given (key, value) pairs:

>>> sorted(x.items(), key=lambda pair: pair[1], reverse=True)[('c', 7), ('a', 5), ('b', 3)]

See the Python sorting howto for more information.

A rather nice addition to @MartijnPieters answer is to get back a dictionary sorted by occurrence since Collections.most_common only returns a tuple. I often couple this with a json output for handy log files:

from collections import Counter, OrderedDictx = Counter({'a':5, 'b':3, 'c':7})y = OrderedDict(x.most_common())

With the output:

OrderedDict([('c', 7), ('a', 5), ('b', 3)]){  "c": 7,   "a": 5,   "b": 3}

Yes:

>>> from collections import Counter>>> x = Counter({'a':5, 'b':3, 'c':7})

Using the sorted keyword key and a lambda function:

>>> sorted(x.items(), key=lambda i: i[1])[('b', 3), ('a', 5), ('c', 7)]>>> sorted(x.items(), key=lambda i: i[1], reverse=True)[('c', 7), ('a', 5), ('b', 3)]

This works for all dictionaries. However Counter has a special function which already gives you the sorted items (from most frequent, to least frequent). It's called most_common():

>>> x.most_common()[('c', 7), ('a', 5), ('b', 3)]>>> list(reversed(x.most_common()))  # in order of least to most[('b', 3), ('a', 5), ('c', 7)]

You can also specify how many items you want to see:

>>> x.most_common(2)  # specify number you want[('c', 7), ('a', 5)]