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Dictionaries & sets

Key–value maps, uniqueness, counting, grouping, and fast lookups.

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How to Count Co-occurrence Pairs in Python with Nested Dictionaries

This code counts how often any two items appear together in the same group, using a nested defaultdict keyed by item pairs.

dictionaries co-occurrence counter
Python 
from itertools import combinations
from collections import defaultdict

def count_cooccurrences(items_per_group):
    cooccurrence = defaultdict(lambda: defaultdict(int))
    for group in items_per_group:
        for a, b in combinations(sorted(group), 2):
            cooccurrence[a][b] += 1
            cooccurrence[b…
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