Lecture-26 2d List_Output 2024-25

Lecture Overview

• Course: COMP101 Introduction to Programming 2023-24

Page 1

• Lecture Topic: 2-D List Output Numbers

• Content: Basic understanding of 2-D lists

Page 2: Nested For Loops

• Example Code:

  list_3x4 = [ [1,2,3,4], [5,6], [7,8,9] ]
  for row in range(len(list_3x4)):
      for column in range(len(list_3x4[row])):
          print(list_3x4[row][column], end=" ")
      print()

• Output Format: Creates a structured output resembling a 2-D list:

  • Result:

    1 2 3 4 5 6 7 8 9

• Explanation:

  • end = " " helps it print on the same line.

  • print() starts a new line after each row has been printed.

  • Indentation and loop structure are crucial to avoid misalignment in outputs.

• Outer and Inner Loops:

  • Outer loop iterates through row indices.

  • Inner loop iterates through column indices.

Page 3: Similar Methods for Output

• Alternative Code Examples:

  list_3x4 = [ [1,2,3,4], [5,6,7,8], [9,10,11,12] ]
  for row in list_3x4:
      for element in row:
          print(element, end = " ")
      print()

• Output Explanation: Same output achieved through different iteration techniques.

• Key Concept: Different structures still utilize the nested for loop.

Page 4: Another Output Example

• Code Snippet:

  num_list = [ [1,2,3], [4,5,6], [7,8,9] ]
  for row in num_list:
      for column in row:
          print(column, end = " ")
      print()

• Details:

  • Use either single or double quotes for string definitions.

  • A space between quotes (" ") creates spacing between numbers in each row.

  • Pay attention to the indentation of the final print statement for formatting.

Page 5: Accessing Rows and Columns

• Example Accessing Code:

  list_out = [ [1,2,3], [4,5,6], [7,8,9] ]
  print(list_out[1])  # Output: [4, 5, 6]
  print(list_out[1][2])  # Output: 6
  print(len(list_out[2]))  # Output: 3

• Explanation:

  • Shows how to access individual rows and elements based on zero-based indexing.

  • Discusses the importance of remembering that indices start from 0.

Page 6: Types of Lists

• Definitions:

  • Dense List:

    • Contains elements mostly or entirely with non-zero values.

    • Example: dense_list = [ [1,2,3], [4,5,6], [7,8,9] ]

  • Sparse List:

    • Contains many zero values amidst some non-zero elements.

    • Example: sparse_list = [ [1,0,3], [0,0,6], [7,0,0] ]

Page 7: Creating a 4x4 Array

• Code for 4x4 Diagonal Matrix:

  list_diag_4x4 = [[0 for row in range(4)] for col in range(4)]
  for i in range(4):
      list_diag_4x4[i][i] = 1

• Output Display:

  • Prints:

    1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1

  • Methodology: Follows three steps:

    1. Creating the list.

    2. Populating the diagonal.

    3. Outputting the list.