In this article, we will discuss how to extract the Kth column from a matrix in Python.

Example:

Matrix = [[4, 5, 6],
[8, 1, 10],
[7, 12, 5]]

The 2nd column (K=2, 0-indexed) would be [6, 10, 5].

Let's look at the different methods below to do it in Python:

Using NumPy

NumPy is a high-performance library for numerical computations. Converting a list of lists into a NumPy array allows vectorized operations, which are faster and more memory-efficient compared to Python loops.

[GFGTABS] Python

import numpy as np
mat = [[4, 5, 6], [8, 1, 10], [7, 12, 5]]
K = 2
res = np.array(mat)[:, K]
print(res)

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Output

[ 6 10 5]

Explanation:

np.array(mat): Converts a list of lists into a NumPy array for efficient operations.
[:, K]: Selects all rows (:) and only the Kth column (K).

Using List Comprehension

Iterates over each row and picks the Kth element. This is clean, Pythonic, and memory-efficient.

[GFGTABS] Python

mat = [[4, 5, 6], [8, 1, 10], [7, 12, 5]]
K = 2
res = [row[K] for row in mat]
print( res)

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Output

[6, 10, 5]

Explanation:

List comprehension: Iterates over each row in matrix.
row[K]: Extracts the Kth element from each row.

Using map()

Applies a lambda function to extract the Kth element from each row. The map() function is slightly less intuitive but works efficiently.

[GFGTABS] Python

mat = [[4, 5, 6], [8, 1, 10], [7, 12, 5]]
K = 2
res = list(map(lambda row: row[K], mat))
print( res)

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Output

[6, 10, 5]

Explanation:

map(): Applies a function to each element of matrix (each row).
lambda row: row[K]: Anonymous function that extracts the Kth element from a row.
list(): Converts the map object into a list.

Using zip()

Transposes the matrix with zip(*) and selects the Kth row of the transposed matrix. This method is readable but slightly slower due to creating intermediate tuples.

[GFGTABS] Python

mat = [[4, 5, 6], [8, 1, 10], [7, 12, 5]]
K = 2

res = list(zip(*mat))[K]
print( res)

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Output

(6, 10, 5)

Explanation:

*mat: Unpacks the matrix rows as separate arguments.
zip(*mat): Transposes the matrix, converting rows into columns.
[K]: Selects the Kth column from the transposed result.
list(): Converts the resulting tuple of elements into a list.

Using a For Loop

Manually iterates through each row, appending the Kth element to a new list. This is simple and beginner-friendly but verbose.

[GFGTABS] Python

mat = [[4, 5, 6], [8, 1, 10], [7, 12, 5]]
K = 2
res = []
for row in mat:
 res.append(row[K])
print( res)

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Output

[6, 10, 5]

Explanation:

for row in mat: Iterates over each row of the matrix.
row[K]: Accesses the element at index K in the current row (the Kth column element).
res.append(row[K]): Adds this element to the result list res.
res: Contains all elements from the Kth column after the loop.

Python | Search in Nth Column of Matrix
Python - Summation of kth column in a matrix

Using NumPy

Using List Comprehension

Using map()

Using zip()

Using a For Loop

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