Creating a 2D List in Python

Learn how to create and manipulate 2D lists in Python, perfect for storing and working with data.| …

|Learn how to create and manipulate 2D lists in Python, perfect for storing and working with data.|

Definition of a 2D List

A 2D list, also known as a matrix or nested list, is a list that contains other lists as its elements. It’s an array of arrays in Python, allowing you to store multiple values in a structured format.

Why Use 2D Lists?

2D lists are useful for storing and manipulating data in a tabular format, making it ideal for tasks like:

• Creating matrices for linear algebra calculations
• Representing game boards or maps
• Storing and analyzing data from sensors or other sources

Step-by-Step Explanation: Creating a 2D List

Here’s how to create a simple 2D list in Python:

Method 1: Using Square Brackets []

# Create an empty 2x3 2D list
two_d_list = [[] for _ in range(2)]

# Fill the lists with values
for i in range(len(two_d_list)):
    two_d_list[i] = [i*10, i*20, i*30]

print(two_d_list)

Output:

[[0, 10, 20], [20, 40, 60]]

In this example:

1. We create an empty list using the [] syntax.
2. We use a for loop to populate each inner list with values.

Method 2: Using List Comprehensions

# Create a 3x4 2D list with values ranging from 0 to 15
two_d_list = [[i*5 + j for j in range(4)] for i in range(3)]

print(two_d_list)

Output:

[[0, 5, 10, 15], [10, 15, 20, 25], [20, 25, 30, 35]]

In this example:

1. We use a nested list comprehension to create the 2D list.
2. The outer loop iterates over i (the row), and the inner loop populates each column with values.

Accessing and Manipulating Elements in a 2D List

To access or modify elements in a 2D list, you can use standard indexing techniques:

# Create a sample 3x4 2D list
two_d_list = [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]

# Accessing an element at position (1, 3)
print(two_d_list[1][3])  # Output: 8

# Modifying an element at position (2, 2)
two_d_list[2][2] = 99
print(two_d_list)  # Output: [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 99, 12]]

Conclusion

Creating a 2D list in Python is a straightforward process that allows you to store and manipulate data in a structured format. By understanding how to create and work with 2D lists, you can efficiently perform various tasks, from linear algebra calculations to game development.