Ps Module 7 – Part II 2D Arrays and LISTS 8/29/2019 CSE 1321 Module 7

2D vs 1D Arrays Still hold several values of the same type (homogeneous) Still based on a slot number (the index number), but has two now Still have instant access Still Static Typically use nested loops to traverse array 8/29/2019 CSE 1321

What 2D Arrays look like . . . . . . 1 2 3 4 5 6 myArray 1 2 3 4 5 6 1 2 3 4 5 6 [0,0] [0,1] [0,2] [0,3] [0,4] [0,5] [0,6] myArray 1 [1,0] [1,1] [1,2] [1,3] [1,4] [1,5] [1,6] 2 [2,0] [2,1] [2,2] [2,3] [2,4] [2,5] [2,6] . . . 3 [3,0] [3,1] [3,2] [3,3] [3,4] [3,5] [3,6] 4 [4,0] [4,1] [4,2] [4,3] [4,4] [4,5] [4,6] 5 [5,0] [5,1] [5,2] [5,3] [5,4] [5,5] [5,6] 6 [6,0] [6,1] [6,2] [6,3] [6,4] [6,5] [6,6] . . . 8/29/2019 CSE 1321

Ps Defining a 2D array CREATE array nums [numRows][numColumns] 8/29/2019 CSE 1321

Java- Define a 2D Array <type> [ ][ ] <name> = new <type>[<rowSize>][<columnSize>]; For example: int[ ][ ] grid = new int [10][20]; 8/29/2019 CSE 1321

C# - Define a 2D Array <type>[ , ]<name> = new <type>[<row_size>,<column_size>]; For example: int[ , ] grid = new int [10,20]; 8/29/2019 CSE 1321

Modifying a 2D Array myArray[2,3] = 42; 1 2 3 4 5 6 myArray 1 2 3 4 5 1 2 3 4 5 6 [0,0] [0,1] [0,2] [0,3] [0,4] [0,5] [0,6] myArray 1 [1,0] [1,1] [1,2] [1,3] [1,4] [1,5] [1,6] 2 [2,0] [2,1] [2,2] [2,3] [2,4] [2,5] [2,6] 3 [3,0] [3,1] [3,2] [3,3] [3,4] [3,5] [3,6] 4 [4,0] [4,1] [4,2] [4,3] [4,4] [4,5] [4,6] 5 [5,0] [5,1] [5,2] [5,3] [5,4] [5,5] [5,6] 6 [6,0] [6,1] [6,2] [6,3] [6,4] [6,5] [6,6] myArray[2,3] = 42; 8/29/2019 CSE 1321

Time for a secret… You use nested loops any time you have to visit every element Find the min Find the max Find the average Print every element etc. It sounds like a test question… Let’s make a multiplication table

CREATE ARRAY grid [4][4]

CREATE ARRAY grid [4][4] 4 4

CREATE ARRAY grid [4][4] How do we initialize this?

FOR each element in a row CREATE ARRAY grid [4][4] FOR each element in a row END FOR row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 1 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 1 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 2 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 2 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 3 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 3 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col row 4 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR row 1 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 1 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 1 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 1 1 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 1 1 row 1

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 2 1 row 1

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 2 1 row 1 2

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 3 1 row 1 2

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 3 1 row 1 2 3

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col row 4 1 row 1 2 3

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR row 2 1 2 3 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 2 1 2 3 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 2 1 2 3 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 1 2 1 2 3 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 1 2 1 2 3 row 2

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 2 2 1 2 3 row 2

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 2 2 1 2 3 row 2 4

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 3 2 1 2 3 row 2 4

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 3 2 1 2 3 row 2 4 6

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col row 4 2 1 2 3 row 2 4 6

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR row 3 1 2 3 2 4 6 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 3 1 2 3 2 4 6 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 3 1 2 3 2 4 6 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 1 3 1 2 3 2 4 6 row

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 1 3 1 2 3 2 4 6 row 3

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 2 3 1 2 3 2 4 6 row 3

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 2 3 1 2 3 2 4 6 row 3 6

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 3 3 1 2 3 2 4 6 row 3 6

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col col row 3 3 1 2 3 2 4 6 row 3 6 9

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR col row 4 3 1 2 3 2 4 6 row 3 6 9

FOR each element in a row FOR each element in a col CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR row 4 1 2 3 2 4 6 3 6 9

CREATE ARRAY grid [4][4] FOR each element in a row FOR each element in a col grid[row, col] = row * col END FOR // Continue processing 1 2 3 2 4 6 3 6 9

Back to your regular lecture… 8/29/2019 CSE 1321 Module 4

Working with 2D arrays Usually involves nested loops, as shown below. Problem Statement: Create an array of 4 rows and 5 columns. Populate the array with the numbers 1-20. --------------------------------------------------------------------- Create array grid[4][5] count ← 1 FOR each element in a row FOR each element in a column     grid[row][col] = count count ← count + 1 END INNER FOR END FOR 8/29/2019 CSE 1321

int count = 1; //declare a 2D array with 4 rows and 5 columns int[][] grid = new int[4][5]; //getting the rows in the array for (int row = 0; row < 4; row++) { //populate the values in the array (row) we're currently on from the outer loop for (int column = 0; column < 5; column++){ grid[row][column] = count; count++; } //for each array in the grid (represented by rows) for(int item[] : grid) //for each element in the array (row) we're currently on from the outer loop for (int number : item) { System.out.print(number + ","); if(number % 5 == 0) { System.out.println(" "); } 8/29/2019 CSE 1321

int count = 1; //declare a 2D array with 4 rows and 5 columns int[,] grid = new int[4, 5]; //getting the rows in the array for (int row = 0; row < 4; row++) { //populate the values in the array (row) we're currently on from the outer loop for (int column = 0; column < 5; column++) grid[row, column] = count; count++; } //for each array in the grid (represented by rows) foreach(int number in grid) //for each element in the array (row) we're currently on Console.Write(number + ","); if(number % 5 == 0) { Console.WriteLine(" "); } 8/29/2019 CSE 1321

multi-dimension arrays CREATE array nums [size_1][size_2][size_3] Use nested loops, one for each dimension to traverse the array FOR each number in the row FOR each number in the column FOR each number in the third dimension do some processing ENDFOR 4/26/2018

C# multi-dimension arrays int[,,] nums= new int [5,6,7]; Example 1: 3 nested loops using GetLength(X)   for(int i=0; i<nums.GetLength(0);i++)   {     for (int j=0; j< nums.GetLength(1);j++)     {      for(int k=0; k<nums.GetLength(2);k++)        {              // do some processing       }     }   } 4/26/2018

C# multi-dimension arrays Example 2: Use a foreach loop as long as you aren’t changing the contents of the array foreach ( int i in nums)  {. . .}  public static int findLargest(int[,,]n)        {            int max = n[0,0,0];             foreach (int j in n)                {                     if( j > max)                        max = j;                }             return max;        } 4/26/2018

Java multi-dimension arrays int[][][] nums= new int [5][6][7]; // 3 nested loops using nums.length, nums[0].length and nums[0][0].length for(int i=0; i<nums.length;i++) {   for (int j=0; j< nums[0].length;j++)   {     for(int k=0; k<nums[0][0].length;k++)     {       // do some processing     }   } } 4/26/2018

Java multi-dimension arrays OR - Use the enhanced for loop/for each loop on each subarray structure, as long as you aren’t changing the contents of the array public static int findLargest3(int[][][]n) {   int max = n[0][0][0];             for ( int [][] e : n ){                 for ( int [] d : e ){                  for ( int i : d ){                         if( i > max)           max = i;                    }     }   }             return max;        } 4/26/2018

Summary 2D Arrays Multi-dimensional Arrays Are like 1D arrays in nature Use nested loops Multi-dimensional Arrays Keep nesting loops for each dimension 8/29/2019 CSE 1321