Nested Lists in Python Code
In Python, nested lists are lists that contain other lists as elements. They are useful for representing structured data like matrices or grids. Here's an overview of how to create and manipulate nested lists in Python.
Creating Nested Lists
You can create nested lists by including lists within a list:
Python Code
# A 2x3 matrix
matrix = [
[1, 2, 3],
[4, 5, 6]
]
Accessing Elements
To access elements in a nested list, you use multiple indices:
Python Code
print(matrix[0][1]) # Output: 2
print(matrix[1][2]) # Output: 6
Modifying Elements
You can modify elements in a nested list by specifying the indices:
Python Code
matrix[0][1] = 9
print(matrix) # Output: [[1, 9, 3], [4, 5, 6]]
Iterating Through Nested Lists
You can use nested loops to iterate through the elements of a nested list:
Python Code
for row in matrix:
for element in row:
print(element)
List Comprehensions with Nested Lists
List comprehensions can be used to create and manipulate nested lists concisely:
Python Code
# Creating a 3x3 matrix with zeros
matrix = [[0 for _ in range(3)] for _ in range(3)]
print(matrix) # Output: [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
# Flattening a nested list
flat_list = [element for row in matrix for element in row]
print(flat_list) # Output: [0, 0, 0, 0, 0, 0, 0, 0, 0]
Example: A 3x3 Matrix Operations
Here is a more detailed example involving a 3x3 matrix:
Python Code
# Creating a 3x3 matrix
matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
# Accessing an element
print("Element at (2, 3):", matrix[1][2]) # Output: 6
# Modifying an element
matrix[2][1] = 10
print("Modified matrix:", matrix)
# Iterating through the matrix
print("Iterating through matrix:")
for row in matrix:
for element in row:
print(element, end=' ')
print()
# Flattening the matrix
flat_list = [element for row in matrix for element in row]
print("Flattened list:", flat_list)
Multidimensional Lists
For more complex structures, you can have lists of lists of lists, and so on:
Python Code
# A 2x2x2 cube
cube = [
[
[1, 2],
[3, 4]
],
[
[5, 6],
[7, 8]
]
]
# Accessing an element
print(cube[0][1][1]) # Output: 4
Nested lists provide a flexible way to manage and manipulate complex data structures in Python. The key is understanding how to access, modify, and iterate through the elements at different levels of nesting.
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