1. Ps
Module 7 – Part II
2D Arrays and LISTS
5/26/2019
CSE 1321 Module 7

2. 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
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CSE 1321

3. What 2D Arrays look like . . . . . . 1 2 3 4 5 6 myArray 1 2 3 4 5 61 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] . . .
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CSE 1321

4. Ps Defining a 2D array CREATE array nums [numRows][numColumns]
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CSE 1321

5. Java- Define a 2D Array
<type> [ ][ ] <name> = new <type>[<rowSize>][<columnSize>];
For example:
int[ ][ ] grid = new int [10][20];
5/26/2019
CSE 1321

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

7. Python – Define a 2D Array
In Python, 2D Arrays must be initialized when they are created. numbers = [[1,2,3,4,5], [6,7,8,9,10], [11,12,13,14,15], [16,17,18,19,20]]
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CSE 1321

8. Modifying a 2D Array myArray[2,3] = 42; 1 2 3 4 5 6 myArray 1 2 3 4 51 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;
5/26/2019
CSE 1321

9. 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

10. CREATE ARRAY grid [4][4]

11. CREATE ARRAY grid [4][4] 4 4

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

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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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

39. 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

40. 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

41. 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

42. 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

43. 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

44. 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

45. 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

46. 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

47. 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

48. 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

49. 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

50. 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

51. 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

52. 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

53. 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

54. 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

55. Back to your regular lecture…
5/26/2019
CSE 1321 Module 4

56. 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
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CSE 1321

57. Working with 2D arrays class Main {
public static void main(String[] args) {
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(" "); }
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CSE 1321

58. Working with 2D arrays using System; class MainClass {
public static void Main (string[] args) {
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(" "); }
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CSE 1321

59. Working with 2D arrays from array import *
numbers = [[1,2,3,4,5], [6,7,8,9,10], [11,12,13,14,15], [16,17,18,19,20]]
for r in numbers:
for c in r:
print(c, end = " ")
print()
#what value does this line print?
print(numbers[3][4])
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CSE 1321

60. List Basics
Most languages provide dynamic structures that can be used to store data. C# and Java provide the ArrayList, while Python provides the List. Following are a few of the differences between the two:
Array List
Array
Can increase and decrease in size dynamically; auto-resize slows performance
Capacity is fixed
Can have only one dimension
Can have multiple dimensions
Provides methods to add, insert, or remove a range
Can work with only one element at a time
Elements of ArrayList are of type Object; therefore, boxing and unboxing typically occur when you store or retrieve a value type
Can store primitives or objects
Length is provided by the size() method
Array uses the length field to determine size
Add elements is accomplished through add method
Can add elements using the index and assignment operator
References to objects are contiguous, but objects are not
Elements are stored contiguously
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CSE 1321

61. Working with Array Lists
import java.util.ArrayList;
class Main {
public static void main(String[] args) {
//declare variables
int n = 2;
//create list
ArrayList<String> colors = new ArrayList<String>(n);
//add colors
colors.add("purple");
colors.add("pink");
colors.add("green");
System.out.println("Does the arraylist contain the color pink?");
if (colors.contains("pink")) {
System.out.println("Yes");
System.out.println("\n");
} else {
System.out.println("No"); }
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CSE 1321

62. Working with Array Lists
CONTINUED FROM PREVIOUS SLIDE
//indexOf returns the position of the argument
System.out.println("Which position is pink in?");
System.out.println(colors.indexOf("pink"));
System.out.println("\n");
//remove removes the argument from the list
colors.remove("purple");
//get() references the position in the arraylist
System.out.println("The item in index 1 of the list is:");
System.out.println(colors.get(1));
//items are stored as objects and can be referenced as such
System.out.println("The Colors Arraylist:");
for(Object o : colors) {
System.out.println(o); }
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CSE 1321

63. Working with Array Lists
using System;
using System.Collections;
class MainClass {
public static void Main (string[] args) {
//create list
ArrayList colors = new ArrayList();
//add colors
colors.Add("purple");
colors.Add("pink");
colors.Add("green");
//contains returns a boolean if list contains argument
Console.WriteLine("Does the arraylist contain the color pink?");
if (colors.Contains("pink")) {
Console.WriteLine("Yes");
Console.WriteLine("\n");
} else {
Console.WriteLine("No"); }
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CSE 1321

64. C# - Working with Array Lists
CONTINUED FROM PREVIOUS SLIDE
//indexOf returns the position of the argument
Console.WriteLine("Which position is pink in?");
Console.WriteLine(colors.IndexOf("pink"));
Console.WriteLine("\n");
//remove removes the argument from the list
colors.Remove("purple");
//can reference by position in the array
Console.WriteLine("The item in index 1 of the list is:");
Console.WriteLine(colors[1]);
//items are stored as objects and can be referenced as such
Console.WriteLine("The Colors Arraylist:");
foreach (Object o in colors) {
Console.WriteLine(o); }
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CSE 1321

65. Python - Working with Lists
colors = list()
#add colors
colors.append('purple')
colors.append('pink')
colors.append('green')
#find if list contains an element
if('pink' in colors):
print('pink is in the list')
print('\n')
#show the index of pink
print(colors.index('pink'))
#remove a color
colors.remove('green')
#output list
for x in range(len(colors)):
print (colors[x])
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CSE 1321

66. Summary 2D Arrays Lists Are like 1D arrays in nature Use nested loops
Have only 1 dimension
Are dynamic: They can grow and shrink
Come with a host of function (add, delete, etc)
5/26/2019
CSE 1321