Day 19: 2D Lists and Nested Loops

Learning Objectives

• AAP-1.C: Represent a list or string using a variable.
• AAP-2.M: For algorithms involving elements of a list: Write iteration statements to traverse a list.
• AAP-2.N: For list operations: Write expressions that use list indexing and list procedures.
• AAP-2.O: For algorithms involving elements of a list: Determine the result of an algorithm that includes list traversals.

Essential Questions

• How do we represent and process two-dimensional data using lists?
• How do nested loops allow us to work with multi-dimensional data structures?

Materials Needed

• Presentation slides on 2D lists and nested loops
• Programming environment
• 2D list manipulation worksheet
• Grid-based problem scenarios
• Exit ticket templates

Vocabulary

• 2D list
• Nested list
• Matrix
• Grid
• Row
• Column
• Nested loop
• Outer loop
• Inner loop
• Multi-dimensional data

Procedure (50 minutes)

Opening (8 minutes)

1. Review and Connection (3 minutes)

   • Review list traversal from previous lesson
   • Connect to today's focus on representing and processing 2D data

2. Warm-up Activity (5 minutes)

   • Present a real-world scenario involving 2D data (e.g., seating chart, game board)
   • Ask students how they might represent this data using lists
   • Introduce the concept of lists containing other lists

Main Activities (32 minutes)

3. Lecture: 2D Lists/Arrays and Nested Data Structures (12 minutes)

   • Define 2D lists as lists containing other lists
   • Explain how 2D lists represent tabular or grid-based data:
     • Rows and columns
     • Coordinates (row, column)
     • Real-world examples (game boards, spreadsheets, images)
   • Demonstrate creating 2D lists:
     • grid ← [[value1, value2], [value3, value4], ...]
     • Visualizing the structure as a grid
   • Explain accessing elements in 2D lists:
     • Using two indices: grid[row][column]
     • Understanding row-major order
   • Discuss modifying elements in 2D lists
   • Introduce nested loops for processing 2D lists:
     • Outer loop for rows
     • Inner loop for columns
     • How nested loops traverse the entire structure
   • Explain common operations on 2D lists:
     • Initializing a grid
     • Accessing all elements
     • Finding values
     • Calculating row/column sums
     • Transforming the grid

4. Demo: Creating and Accessing 2D List Elements (8 minutes)

   • Walk through examples of working with 2D lists:
     • Creating a 2D list representing a game board
     • Accessing specific elements by row and column
     • Modifying elements in the grid
     • Traversing the entire grid with nested loops
     • Processing rows or columns individually
   • Demonstrate common patterns for 2D list manipulation:
     • Initializing a grid of a specific size
     • Finding values in a grid
     • Calculating statistics for rows or columns
     • Transforming the entire grid
   • Show how to visualize 2D lists for better understanding
   • Highlight common errors and pitfalls

5. Hands-on: Manipulating 2D Lists (12 minutes)

   • Students work in the programming environment
   • Guide students through creating and manipulating 2D lists
   • Have students implement programs that:
     • Create and initialize 2D lists
     • Access and modify elements by position
     • Traverse the grid using nested loops
     • Perform calculations on rows or columns
     • Implement simple grid-based algorithms
   • Encourage students to visualize their 2D lists as grids
   • Challenge students to solve problems requiring 2D data representation

Closing (10 minutes)

6. Activity: Implementing a Grid-Based Application (5 minutes)

   • Students design and implement a simple grid-based application
   • Application ideas:
     • Simple game board (tic-tac-toe, minesweeper)
     • Seating chart manager
     • Image representation (using numbers for colors)
     • Simple spreadsheet
   • Share and discuss different implementations
   • Highlight effective use of 2D lists and nested loops

7. Exit Ticket and Preview (5 minutes)

   • Students develop a program that effectively uses 2D lists
   • Preview that next class will focus on other collection types

Assessment

• Formative: Quality of 2D list manipulation during hands-on activities
• Exit Ticket: Correctness and efficiency of program using 2D lists

Differentiation

For Advanced Students

• Challenge them with more complex grid-based problems
• Introduce algorithms that operate on 2D structures (e.g., flood fill)
• Have them implement more sophisticated grid-based applications

For Struggling Students

• Provide templates for 2D list creation and traversal
• Use visual aids to illustrate the structure of 2D lists
• Focus on simpler grid operations before moving to complex ones

Homework/Extension

• Complete a worksheet with 2D list manipulation exercises
• Enhance the grid-based application started in class
• Research real-world applications of 2D data structures

Teacher Notes

• Emphasize the connection between 2D lists and real-world grid-based data
• Watch for confusion about the order of indices (row, then column)
• Make connections to mathematical concepts like matrices
• Consider using graph paper to visualize 2D lists
• Remind students that nested loops are a powerful tool for processing 2D data