How to count occurrence of items in a list in Python?

Question

lets say:

 a = [1,1,2,2,3,3,3,3,4,4,4,4]

b is dict

I want b as dict which represents number of occurrence of items in a:
I want jinja2 template that create output as below.

Output of b should be, ( key - itemName, Value - corresponding item occurrence in list)

Is it possible to do via jinja2 template - i have jinja engine which renders some output i want to add this kind of stuff in template.

Please edit your question to explain how your post relates to `jinja2`. — Corentin Pane, Nov 10 '19 at 12:09

score 2 · Answer 1 · answered Nov 10 '19 at 12:04

You can use collection.Counter to perform these operations efficiently:

from collections import Counter
a = [1,1,2,2,3,3,3,3,4,4,4,4] 
result = dict(Counter(a)) # {1: 2, 2: 2, 3: 4, 4: 4}

for index, value in result.items():
    print(str(index) + " : " + str(value))

score -1 · Answer 2 · answered Nov 10 '19 at 12:01

-1

count_dict = {i:a.count(i) for i in set(a)}

is that what you asked for?

answered Nov 10 '19 at 12:01

music_junkie

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This works, but will lose the order of the list elements. – James Nov 10 '19 at 12:04

score -1 · Answer 3 · answered Nov 10 '19 at 12:58

-1

You can also do this:

a = [1,1,2,2,3,3,3,3,4,4,4,4] 
frequency = {}
for i  in range(len(a)):
    frequency[a[i]] = a.count(a[i])
print(frequency)

answered Nov 10 '19 at 12:58

Sheri

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How to count occurrence of items in a list in Python?

3 Answers3