python 33 lines · 8 steps

Counting things with collections.Counter

A tour of Counter's tallying, merging, comparison, and expansion tricks through small helper functions.

Explained by highlit

Beginner counting multiset data-structures standard-library

1from collections import Counter
2 
3 
4def word_frequencies(text):
5    words = text.lower().split()
6    return Counter(words)
7 
8 
9def char_histogram(text):
10    counts = Counter(c for c in text if c.isalpha())
11    return counts
12 
13 
14def merge_counts(a, b):
15    combined = Counter(a)
16    combined.update(b)
17    return combined
18 
19 
20def difference(a, b):
21    return Counter(a) - Counter(b)
22 
23 
24def top_n(items, n):
25    return Counter(items).most_common(n)
26 
27 
28def has_same_multiset(a, b):
29    return Counter(a) == Counter(b)
30 
31 
32def elements_with_repetition(counts):
33    return list(Counter(counts).elements())

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Counter turns any iterable into a tally dict where missing keys default to zero.
2Arithmetic and comparison operators let you treat Counters as multisets, not just dicts.
3Methods like most_common and elements expose ranking and re-expansion without manual loops.

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