How to reduce on a list of tuples in python

Question

I have an array and I want to count the occurrence of each item in the array.

I have managed to use a map function to produce a list of tuples.

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Answer 1

If all you need is cnt, then a dict would probably be better than a list of tuples here (if you need this format, just use dict.items).

The collections module has a useful data structure for this, a defaultdict.

from collections import defaultdict
cnt = defaultdict(int) # create a default dict where the default value is
                       # the result of calling int
for key in arr:
  cnt[key] += 1 # if key is not in cnt, it will put in the default

# cnt_list = list(cnt.items())