In Python, we often need to work with more complex structures than simple lists. One such structure is a 2D list, also called a matrix. A 2D list is essentially a list of lists, allowing you to organise data in rows and columns, much like a table or spreadsheet.

In other programming languages, a similar concept is called a 2D array, where data is stored in a grid of rows and columns. In Python, although we don’t have traditional arrays, 2D lists provide a flexible and powerful way to represent data in a tabular form.

• 1D List: A single list that contains a sequence of values.
• 2D List (Matrix): A list where each element is itself a list, allowing us to represent data in rows and columns.

Real-World Example:

Think about a simple spreadsheet where each row represents a different student, and each column represents the scores they achieved in different subjects. This kind of structured data can be easily stored and manipulated using a 2D list in Python.

Creating 2D Lists:

You can create a 2D list by nesting lists inside a main list. Each inner list represents a row of data, and you can access elements using two indices—one for the row and one for the column.

Here’s a basic example:

# A 2D list representing a table of numbers
matrix = [ [1, 2, 3], [4, 5, 6], [7, 8, 9] ]

In this example, the outer list contains three inner lists, each representing a row of numbers.

 

Accessing Elements in a 2D List:

You can access elements in a 2D list using two indices:

1. The first index selects the row.
2. The second index selects the column within that row.

For example, to access the number 6 in the matrix:

 print(matrix[1][2])

Here, matrix[1] accesses the second row ([4, 5, 6]), and matrix[1][2] accesses the third element (6) in that row. The output will be:

6

 

Adding (Appending) to a 2D List:

You can add new rows to a 2D list using the append() method. This adds an entire new row (which is a list) at the end of the matrix.

For example:

# Adding a new row to the matrix
matrix.append([10, 11, 12]) print(matrix)

Now, the matrix will have four rows:

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

Removing Items from a 2D List:

You can remove an entire row from the matrix using the pop() method. If you want to remove the second row (index 1), you would do the following:

# Removing the second row from the matrix
matrix.pop(1)
print(matrix)

After removing the second row, the matrix will look like this:

[[1, 2, 3],
[7, 8, 9],
[10, 11, 12]]

To remove specific elements from a row, you can use del. For example, to remove the second element (2) from the first row:

# Removing the second element from the first row
del matrix[0][1] print(matrix)

The updated matrix will be:

[[1, 3],
[7, 8, 9],
[10, 11, 12]]

Modifying Elements in a 2D List:

You can modify specific elements in a 2D list by accessing them with their row and column indices. For example, to change the value 9 in the matrix to 99:

# Changing the value of 9 to 99
matrix[1][2] = 99
print(matrix)

The modified matrix will be:

[[1, 3],
[7, 8, 99],
[10, 11, 12]]

By understanding how to create, access, add to, remove from, and modify 2D lists in Python, you can handle more complex data structures, such as tables, grids, and matrices, with ease.