How to sort Counter by value? - python

Other than doing list comprehensions of reversed list comprehension, is there a pythonic way to sort Counter by value? If so, it is faster than this:

    >>> from collections import Counter
    >>> x = Counter({'a':5, 'b':3, 'c':7})
    >>> sorted(x)
    ['a', 'b', 'c']
    >>> sorted(x.items())
    [('a', 5), ('b', 3), ('c', 7)]
    >>> [(l,k) for k,l in sorted([(j,i) for i,j in x.items()])]
    [('b', 3), ('a', 5), ('c', 7)]
    >>> [(l,k) for k,l in sorted([(j,i) for i,j in x.items()], reverse=True)]
    [('c', 7), ('a', 5), ('b', 3)

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.

From: stackoverflow.com/q/20950650