sorting – How to sort Counter by value? – python

sorting – How to sort Counter by value? – python

Use the Counter.most_common() method, itll 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)]

Itll 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, OrderedDict

x = 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
}

sorting – How to sort Counter by value? – python

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). Its 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)]