Counting elements with dictionary

Wed, Feb 26, 2014

Let’s say you want to find how many times each element is present in the list or tuple.

Normal approach

words = ['a', 'the', 'an', 'a', 'an', 'the']
d = {}
for word in words:
    if word in d:
        d[word] += 1
    else:
        d[word] = 1
print d
{'a': 2, 'the': 2, 'an': 2} 

Better approach

words = ['a', 'the', 'an', 'a', 'an', 'the']
d = {}
for word in words:
    d[word] = d.get(word, 0) + 1

print d
{'a': 2, 'the': 2, 'an': 2

Both the approach returned same values. The first one has 6 lines of logic and second has 3 lines of logic (less code less management).

Second approach uses d.get method. d.get(word, 0) return count of the word if key is present else 0. If 0 isn’t passed get will return None.

Pythonic approach:

import collections

words = ['a', 'b', 'a']

res = collections.Counter(words)

print res
Counter({'a': 2, 'b': 1})

Last approach is just one line and pythonic.

Snippet is extracted from Transforming Code into Beautiful, Idiomatic Python. Do watch and enjoy.