Python - Count the frequency of matrix row length

When working with matrices (lists of lists), you may need to count how many rows have the same length. Python provides several approaches to count the frequency of matrix row lengths using dictionaries or the Counter class.

Using Dictionary with Manual Counting

The traditional approach iterates through the matrix and manually tracks row length frequencies ?

matrix = [[42, 24, 11], [67, 18], [20], [54, 10, 25], [45, 99]]

print("The matrix is:")
print(matrix)

frequency = {}
for row in matrix:
    length = len(row)
    if length not in frequency:
        frequency[length] = 1
    else:
        frequency[length] += 1

print("Row length frequency:")
print(frequency)

The matrix is:
[[42, 24, 11], [67, 18], [20], [54, 10, 25], [45, 99]]
Row length frequency:
{3: 2, 2: 2, 1: 1}

Using Counter from collections

The Counter class provides a more concise solution for counting frequencies ?

from collections import Counter

matrix = [[42, 24, 11], [67, 18], [20], [54, 10, 25], [45, 99]]

# Count frequencies of row lengths
row_lengths = [len(row) for row in matrix]
frequency = Counter(row_lengths)

print("Row length frequency:")
print(dict(frequency))

Row length frequency:
{3: 2, 2: 2, 1: 1}

Using Dictionary get() Method

The get() method simplifies the counting logic by providing a default value ?

matrix = [[1, 2, 3, 4], [5, 6], [7], [8, 9, 10], [11, 12]]

frequency = {}
for row in matrix:
    length = len(row)
    frequency[length] = frequency.get(length, 0) + 1

print("Row length frequency:")
for length, count in sorted(frequency.items()):
    print(f"Length {length}: {count} rows")

Row length frequency:
Length 1: 1 rows
Length 2: 2 rows
Length 4: 2 rows

Comparison

Conclusion

Use Counter from collections for the most readable and efficient solution. The manual dictionary approach helps understand the underlying logic, while get() method offers a clean middle ground.