CODEWITHSUNDEEP
pythonlistcount
James Xiang
James Xiang

Reputation: 137

Counting number of occurrence across lists

I have 3 lists with all unique elements in each and I want to count the number of occurrence for each element. Unique here means all the elements in a list are unique, no duplicated ones.

An example of the data:

list(c[0]):       list(c[1]):       list(c[1]):      
a                 a                 a
b                 b                 b
c                 c
d

And so the desired output should be 

a:3,b:3,c:2,d:1

I understand that Counter can be applied to within one list, but how do I calculate across lists?

Upvotes: 1

Views: 78

Answers (3)

Sunitha
Sunitha

Reputation: 12015

Use chain.from_iterable to convert the list to a flat list and then feed it to Counter

from collections import Counter
from itertools import chain
c = [['a', 'b', 'c', 'd'], ['a', 'b'], ['a']]
Counter(chain.from_iterable(c))
# Counter({'a': 3, 'b': 2, 'c': 1, 'd': 1})

Upvotes: 0

blhsing
blhsing

Reputation: 106553

Merge the 3 lists with itertools.chain and then use collections.Counter to count the items.

from collections import Counter
from itertools import chain
c = [['a', 'b', 'c', 'd'], ['a', 'b'], ['a']]
print(dict(Counter(chain(*c))))

This outputs:

{'a': 3, 'b': 2, 'c': 1, 'd': 1}

Upvotes: 0

Primusa
Primusa

Reputation: 13498

Flatten the list and then use counter:

Assuming lst is a list of the three lists in question:

flat = [i for sub in lst for i in sub]
Counter(flat)

Upvotes: 3

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