Nested lists (Two dimensional lists for Python)

Two dimensional lists
(arrays)

• https://www.scaler.com/topics/2d-array-in-python/
• https://snakify.org/en/lessons/two_dimensional_lists_arrays/
• https://www.geeksforgeeks.org/python-using-2d-arrays-lists-the-right
-way/

• Two Dimensional (2D) lists in Python is a nested data structure,
meaning it is a set of lists inside another list. The 2D list is mostly
used to represent data in a tabular or two-dimensional format.

• A 2D array in python is a two-dimensional data structure used for
storing data generally in a tabular format. For example, if you want to
store a matrix and do some computations, how would you do it in
Python?

Syntax of Python 2D Array
• Each element in a 2D array is represented by two indices, the row and
the column. 2D arrays in python are zero-indexed, which means
counting indices start from zero rather than one; thus, zero is the first
index in an array in python.

Syntax of Python 2D Array
• array_name=[[r1c1,r1c2,r1c3,..],[r2c1,r2c2,r2c3,...],. . . .]
• Where array_name is the array's name, r1c1, r1c1 etc., are elements
of the array. Here r1c1 means that it is the element of the first column
of the first row. A 2D array is an array of arrays.
• Example:
• # Define the two-dimensional list
• array_name = [ [1, 2, 3], [4, 5, 6], [7, 8, 9] ]

Accessing Values in Python 2D Array
• We can directly access values or elements of a 2D array in Python. It
can be done by using the row and column indices of the element to
be accessed. It has the following syntax:
• array_name[row_ind][col_ind]
• EX: # Accessing elements
• array_name = [ [1, 2, 3], [4, 5, 6], [7, 8, 9] ]
• print("Element at row 1, column 1:", array_name[0][0]) # Output: 1
print("Element at row 2, column 3:", array_name[1][2]) # Output: 6
print("Element at row 3, column 2:", array_name[2][1]) # Output: 8

• If an index exceeds the size, if the array is provided to this function, it
returns the index out of range error. Such indices are known as out
of bounds.

Traversing Values in Python 2D Array
• Traversing in a 2D array in python can be done by using a for a loop.
We can iterate through the outer array first, and then at each element
of the outer array, we have another array, our internal array
containing the elements. So for each inner array, we run a loop to
traverse its elements.

Inserting Values in Python 2D Array
• Inserting a value in an array means adding a new element at a given
index in the array and then shifting the remaining elements
accordingly.
1. Adding a New Element in the Outer Array.
arr1.insert(ind,arr_insert)
2. Adding a New Element in the Inner Array.
arr1[r].insert(ind,arr_insert)

Example of inserting values to outer value

Nested lists (Two dimensional lists for Python)

Inserting value to the inner list

Updating Values in Python 2D Array
• arr_name[r][c]=new_element
• It Single element and inner list update types
• Example: arr[1][2]=16 will update single element of list

Updating inner list
• If you want to update inner list
• new_arr=[10,11,12]
• arr[1]=new_arr

Nested lists (Two dimensional lists for Python)

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