return the top n most frequently occurring chars and their respective counts in python

Question

how to return the top n most frequently occurring chars and their respective counts # e.g \'aaaaaabbbbcccc\', 2 should return [(\'a\', 6), (\'b\'

Answer 1

Use collections.Counter(); it has a most_common() method that does just that:

>>> from collections import Counter
>>> counts = Counter('aaaaaabbbbcccc')
>>> counts.most_common(2)
[('a', 6), ('c', 4)]

Note that for both the above input and in aabc both b and c have the same count, and both can be valid top contenders. Because both you and Counter sort by count then key in reverse, c is sorted before b.

If instead of sorting in reverse, you used the negative count as the sort key, you'd sort b before c again:

list4.sort(key=lambda v: (-v[1], v[0))

Not that Counter.most_common() actually uses sorting when your are asking for fewer items than there are keys in the counter; it uses a heapq-based algorithm instead to only get the top N items.

Answer 2

A little harder, but also works:

text = "abbbaaaa"

dict = {}
for lines in text:
    for char in lines:
        dict[char] = dict.get(char, 0) + 1

print dict