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Creating two-dimensional arrays in Python
Two-dimensional arrays in Python are lists of lists, where each nested list is a row of a matrix. This data structure is widely used for working with matrices, tables, and two-dimensional coordinate systems.
Static creation of a two-dimensional array
The easiest way to create a two-dimensional array is to declare it explicitly:
matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
Creating an empty two-dimensional array
A list generator is used to create an empty two-dimensional fixed-size array:
rows, cols = 3, 3
matrix = [[0 for _ in range(cols)] for _ in range(rows)]
print(matrix) # [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
Important: Avoid creating an array using [[0] * cols] * rows, as this will create references to the same object.
Initialization with the specified value
rows, cols = 3, 3
initial_value = 1
matrix = [[initial_value for _ in range(cols)] for _ in range(rows)]
print(matrix) # [[1, 1, 1], [1, 1, 1], [1, 1, 1]]
Creation from a string
A useful way to create a two-dimensional array from a formatted string:
input_string = "1,2,3 4,5,6 7,8,9"
rows = input_string.split(' ')
two_dimensional_array = [list(map(int, row.split(','))) for row in rows]
print(two_dimensional_array) # [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
Creating using NumPy
For more complex operations, we recommend using the NumPy library:
import numpy as np
# Creating a null array
matrix = np.zeros((3, 3))
# Creating a unit matrix
identity = np.eye(3)
# Create from a regular list
matrix = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
Access to the elements of a two-dimensional array
Reading the element
Double indexing is used to access the element:
matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
print(matrix[1][2]) # 6 ( second line, third element)
Changing the element
matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
matrix[1][2] = 10
print(matrix) # [[1, 2, 3], [4, 5, 10], [7, 8, 9]]
Getting a row or column
matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
# Getting the row
row = matrix[1] # [4, 5, 6]
# Getting column
column = [row[1] for row in matrix] # [2, 5, 8]
Iterating over a two-dimensional array
Iterating over lines
matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
for row in matrix:
print(row)
Iterating over elements with indexes
two_dimensional_array = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
for i in range(len(two_dimensional_array)):
for j in range(len(two_dimensional_array[i])):
print(f"The element at position ({i}, {j}) is equal to {two_dimensional_array[i][j]}")
Iterating with enumerate
matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
for i, row in enumerate(matrix):
for j, element in enumerate(row):
print(f"matrix[{i}][{j}] = {element}")
Basic operations with two-dimensional arrays
Matrix transposition
matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
transposed = [[matrix[j][i] for j in range(len(matrix))] for i in range(len(matrix[0]))]
print(transposed) # [[1, 4, 7], [2, 5, 8], [3, 6, 9]]
# Alternative way with zip
transposed = list(map(list, zip(*matrix)))
Search for the maximum and minimum element
matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
max_value = max(max(row) for row in matrix)
min_value = min(min(row) for row in matrix)
print(f"Maximum element: {max_value}") #9
print(f"Minimum element: {min_value}") # 1
Sum of all elements
matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
total_sum = sum(sum(row) for row in matrix)
print(f"Sum of all elements: {total_sum}") # 45
Sum by rows and columns
matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
#
row_sums row sum = [sum(row) for row in matrix]
print(f"Row sum: {row_sums}") # [6, 15, 24]
# Sum by columns
col_sums = [sum(matrix[i][j] for i in range(len(matrix))) for j in range(len(matrix[0]))]
print(f"Sum by columns: {col_sums}") # [12, 15, 18]
Two-dimensional array generators
Generating a matrix of products
rows, cols = 3, 3
matrix = [[i * j for j in range(cols)] for i in range(rows)]
print(matrix) # [[0, 0, 0], [0, 1, 2], [0, 2, 4]]
Chessboard generation
rows, cols = 3, 3
matrix = [[(i + j) % 2 for j in range(cols)] for i in range(rows)]
print(matrix) # [[0, 1, 0], [1, 0, 1], [0, 1, 0]]
Generating a unit matrix
size = 3
identity = [[1 if i == j else 0 for j in range(size)] for i in range(size)]
print(identity) # [[1, 0, 0], [0, 1, 0], [0, 0, 1]]
Useful functions for working with two-dimensional arrays
Checking the square matrix
def is_square(matrix):
return len(matrix) == len(matrix[0]) if matrix else False
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
print(is_square(matrix)) # True
Rotation of the matrix by 90 degrees
def rotate_90(matrix):
return [[matrix[j][i] for j in range(len(matrix)-1, -1, -1)] for i in range(len(matrix[0]))]
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
rotated = rotate_90(matrix)
print(rotated) # [[7, 4, 1], [8, 5, 2], [9, 6, 3]]
Smoothing a two-dimensional array
def flatten(matrix):
return [element for row in matrix for element in row]
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
flat = flatten(matrix)
print(flat) # [1, 2, 3, 4, 5, 6, 7, 8, 9]
Two-dimensional arrays in Python provide a flexible tool for working with tabular data and matrices. For more complex mathematical operations, it is recommended to use specialized libraries such as NumPy or Pandas.