Simplest way to find the element that occurs the most in each column

Question

Suppose I have

data =
[[a, a, c],
 [b, c, c],
 [c, b, b],
 [b, a, c]]

I want to get a list containing the element that occurs the most in each

Answer 1

Is the data hashable? If so, a collections.Counter will be helpful:

[Counter(col).most_common(1)[0][0] for col in zip(*data)]

It works because zip(*data) transposes the input data yielding 1 column at a time. The counter then counts the elements and stores the counts in a dictionary with the counts as values. Counters also have a most_common method which returns a list of the "N" items with the highest counts (sorted from most counts to least counts). So, you want to get the first element in the first item in the list returned by most_common which is where the [0][0] comes from.

e.g.

>>> a,b,c = 'abc'
>>> from collections import Counter
>>> data = [[a, a, c],
...  [b, c, c],
...  [c, b, b],
...  [b, a, c]]
>>> [Counter(col).most_common(1)[0][0] for col in zip(*data)]
['b', 'a', 'c']