Develop Reference

Creating a matrix from a text file - Java

I have this text file:
2
2
12
13
23
24
49
59
69
79
the first two numbers should be the rows and columns of the matrix, which is 2x2 in this case. My issue that I'm trying to get around is finding a way to include a second 2D array that holds the second matrix.
my code:
Scanner fileInput = new Scanner(new File("input1.txt"));
int n1 = fileInput.nextInt();
int n2 = fileInput.nextInt();
System.out.print("matrix is " + n1 + "x" + n2 +"\n");
int [][] firstMatrix = new int [n1][n2];
int [][] secondMatrix = new int [n1][n2];
for(int i = 0; i < n1; ++i)
{
for(int j = 0; j < n2; ++j)
{
if(fileInput.hasNextInt())
{
firstMatrix[i][j] = fileInput.nextInt();
}
}
}
System.out.println("Matrices: ");
for(int i = 0; i < n1; i++)
{
for(int j = 0; j < n2; j++)
{
System.out.println(firstMatrix[i][j]);
}
}
it only prints the following:
12
13
23
24
How do I make it read the next four lines of integers from the file? It would also be helpful to understand how I can make it look something like this:
12 13
23 24
EDIT: This approach seemed to help with the last question:
for(int i=0; i<n1; i++)
{
for(int j=0; j<n2; j++)
{
System.out.print(firstMatrix[i][j] + " " );
//System.out.print(secondMatrix[i][j] + " ");
}
System.out.println();
}
The only problem I'm facing now is being able to include the four other integers and turn them into a matrix.

You can group them to 1 array:
int matrixNumb = 2; // number of matrix
int [][][] matrix = new int [matrixNumb][n1][n2];
for (int h = 0; h < matrixNumb; h++)
{
for(int i = 0; i < n1; ++i)
{
for(int j = 0; j < n2; ++j)
{
if(fileInput.hasNextInt())
{
matrix [h][i][j] = fileInput.nextInt(); // read from file
}
}
}
}
System.out.println("Matrices: ");
for (int h = 0; h < matrixNumb; h++)
{
for(int i = 0; i < n1; i++)
{
for(int j = 0; j < n2; j++)
{
System.out.print(matrix[h][i][j]);
System.out.print("\t"); //How do you want to separate columns?
}
System.out.print("\r\n"); //How do you want to separate rows?
}
System.out.println(); //How do u want to print next matrix?
}
I have not compiled or run it, but hope it help.

You can just read data for the two arrays from file sequentially, like this:
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class App {
private static void readMatrix(final Scanner scanner, final int[][] matrix) {
for (int i = 0; i < matrix.length; ++i) {
for (int j = 0; j < matrix[i].length; ++j) {
if (scanner.hasNextInt()) {
matrix[i][j] = scanner.nextInt();
}
}
}
}
private static void displayMatrix(final int[][] matrix) {
for (int i = 0; i < matrix.length; i++) {
for (int j = 0; j < matrix[i].length; j++) {
System.out.print(matrix[i][j] + " ");
}
System.out.println();
}
}
public static void main(final String... args) throws FileNotFoundException {
final Scanner scanner = new Scanner(new File("input.txt"));
final int n1 = scanner.nextInt();
final int n2 = scanner.nextInt();
System.out.print(String.format("The matrix is %d x %d \n", n1, n2));
final int[][] firstMatrix = new int[n1][n2];
final int[][] secondMatrix = new int[n1][n2];
System.out.println("Reading data to first matrix");
readMatrix(scanner, firstMatrix);
System.out.println("Reading data to second matrix");
readMatrix(scanner, secondMatrix);
System.out.println("First Matrix");
displayMatrix(firstMatrix);
System.out.println("Second Matrix");
displayMatrix(secondMatrix);
}
}

for(int i = 0; i < n1*n1; i++)
{
for(int j = 0; j < n2*n2; j++)
{
if(fileInput.hasNextInt())
{
if(i < n1){
firstMatrix[i][j] = fileInput.nextInt();
}
else
{
secondMatrix[i][j] = fileInput.nextInt();
}
}
}
}
You have two matrix of size n*n so you can do like this:

Convert two 1D arrays into single 2D array

I have 2 1d arrays and i am trying to populate them into a single 2d array in JAVA.
For instance:
a[] = {2,7}
b[] = {9,1}
The results should then be:
result[][] = {{2,9}, {7,1}}
This is my code
import java.util.Arrays;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter Test Cases:\t");
int t = sc.nextInt();
int[] a;
int[] b;
int i, j, x;
for (int k = 0; k < t; k++) {
System.out.println("Enter 1st Array Limit:\t");
int len = sc.nextInt();
System.out.println("Enter 2nd Array Limit:\t");
int len1 = sc.nextInt();
a = new int[len];
b = new int[len1];
System.out.println("Enter Sum Value");
x = sc.nextInt();
System.out.println("Enter " + len + " elements:\t");
for (i = 0; i < len; i++) {
a[i] = sc.nextInt();
}
System.out.println("Enter " + len1 + " elements:\t");
for (j = 0; j < len1; j++) {
b[j] = sc.nextInt();
}
int [][] c = new int[len][2];
for (i = 0; i < len; i++) {
for (j = 0; j < len1; j++) {
if (a[i] + b[j] == x) {
for(int l = 0; i < a.length; i++){
c[l][0] = a[i];
c[l][1] = b[j];
}
}
}
}
System.out.println(Arrays.deepToString(c));
}
}
}
This still produces wrong output
i want to find Find all pairs with a given sum

int[] a = {2,7};
int[] b = {9,1};
int[][] c = new int[a.length][2];
for(int i = 0; i < a.length; i++){
c[i][0] = a[i];
c[i][1] = b[i];
}
should do the trick

How to calculate the average of each row and column in array

So yesterday I asked for help, and a lot of people helped me out with my question, I really appreciated that guys. However, I run into a second problem of my homework, and I have been trying to solve it from this morning, and now it's like almost 2AM in the morning, and I'm not gonna sleep until I solve this problem. I'm not going to lie, so this is my homework to test the basic knowledge of mine. I know I make major mistakes somewhere, so please help me to point them out, so I can fix them. Thank you
The output should be:
1, 2, 3, ave=2
4, 5, 6, ave=5
aver=2.5, 3.5, 4.5
This is my current code:
import java.util.Scanner;
public class Ex {
public static void main(String[] args)
{
Scanner input = new Scanner(System.in);
System.out.print("Enter a number for rows: ");
int rows = input.nextInt();
System.out.print("Enter a number for columns: ");
int columns = input.nextInt();
int[][] array = new int[rows][columns];
System.out.println("Enter the numbers in array: ");
for(int i=0 ; i<rows ; i++)
{
for(int j=0 ; j<columns ; j++)
{
array[i][j] = input.nextInt();
}
}
for(int i=0 ; i<rows ; i++)
{
for(int j=0 ; j<columns ; j++)
{
System.out.print(array[i][j] + " , ");
}
System.out.println("\n");
}
}
double averageRow(int[][] array) {
int rowTotal = 0;
double average = 0;
for (int rows = 0; rows < array.length; rows++) {
for (int columns = 0; columns < array[rows].length; columns++) {
rowTotal += array[rows][columns];
}
average = rowTotal / array[rows].length;
System.out.println(average);
rowTotal = 0;
}
return rowTotal;
}
double averageColumn(int[][] array) {
int columnTotal = 0;
double average = 0;
for (int columns = 0; columns < array.length; columns++) {
for (int rows = 0; rows < array[columns].length; rows++) {
columnTotal += array[rows][columns];
}
average = columnTotal / array[columns].length;
System.out.println(average);
columnTotal = 0;
}
return columnTotal;
}
}

public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
System.out.println("Enter number of rows");
int r = sc.nextInt();
System.out.println("Enter number of columns");
int c = sc.nextInt();
System.out.println("Enter values");
int[][] matrix = new int[r][c];
for (int i = 0; i < r; i++)
{
float rowSum = 0f;
for (int j = 0; j < c; j++)
{
matrix[i][j] = sc.nextInt();
rowSum += matrix[i][j];
}
System.out.println("Average of row " + i + " " + rowSum / c);
}
for (int i = 0; i < c; i++)
{
float columnSum = 0f;
for (int j = 0; j < r; j++)
{
columnSum += matrix[j][i];
}
System.out.println("Average of column " + i + " " + columnSum / r);
}
sc.close();
}
You can find the each row sum while reading the data. For column average run loop again. Hope you will sleep :)

You can print without calling other function.
import java.util.Scanner;
public class test8 {
public static void main(String[] args)
{
Scanner input = new Scanner(System.in);
System.out.print("Enter a number for rows: ");
int rows = input.nextInt();
System.out.print("Enter a number for columns: ");
int columns = input.nextInt();
int[][] array = new int[rows][columns];
System.out.println("Enter the numbers in array: ");
for(int i=0 ; i<rows ; i++)
{
for(int j=0 ; j<columns ; j++)
{
array[i][j] = input.nextInt();
}
}
int rowSum = 0;
int colSumArr[] = new int[columns];
for(int i=0 ; i<rows ; i++)
{
for(int j=0 ; j<columns ; j++)
{
rowSum = rowSum + array[i][j];
colSumArr[j] = colSumArr[j] + array[i][j];
System.out.print(array[i][j] + " , ");
}
System.out.println( " ave=" + (double)rowSum/columns);
rowSum = 0;
}
System.out.printf("aver=");
for(int i=0;i<columns;i++){
if(i!=columns -1)
System.out.print((double)colSumArr[i]/rows + ", ");
else
System.out.print((double)colSumArr[i]/rows);
}
}
}

How do i output random numbers for 2 different arrays?

This is what i have so far but the output for both arrays is the same randomly generated numbers instead of different ones for each array.
import java.util.Scanner;
public class Prog2_b {
public static void main(String[] args) {
Scanner scnr = new Scanner(System.in);
System.out.println("Program #2b, Breanna Bergado, mascID 1885");
System.out.println("Please enter number of elements for a 1D array:");
int userVal = scnr.nextInt();
//System.out.println(((Object)userVal).getClass().getName();
double[] array = new double[userVal];
double [] array2 = new double[userVal];
double dotProd = 0;
for(int i = 0; i < userVal; i++) {
array[i] = Math.random();
array2[i] = Math.random();
}
for (int j = 0; j < 2; j++){
System.out.println("a"+(j+1)+"[]");
System.out.println("----------------");
for (int i = 0; i < userVal; i++) {
System.out.println(array[i] + " ");
}
System.out.println();
}
for(int i = 0; i < userVal; i++) {
dotProd = dotProd + array[i]* array2[i];
}
System.out.println("Dot Product is " + dotProd);
}
}

You should update your printing logic to:
for (int i = 0; i < userVal; i++) {
System.out.println(array[i] + " ");
}
System.out.println();
for (int j = 0; j < userVal; j++) {
System.out.println(array2[j] + " ");
}
Your current logic just prints the first array twice. You could also use nested arrays as one of the comments suggested, but the above code will work with what you have so far.

Out of Bounds Error in 2D Array with Dice Program

So I am creating a program that rolls z die x times with y sides, and I keep getting an out of bounds error at the first line in the first for loop. However I'm not sure why this is, the loop counts from 0 to (z-1). I'm basically in the home stretch of this program and I need the help of the stackoverflow community.
public class Ass11f {
public static void main(String[] args) {
EasyReader console = new EasyReader();
System.out.print("Enter how many times you want to roll the die: ");
int x = console.readInt();
System.out.print("Enter the amount of sides: ");
int y = console.readInt();
System.out.print("Enter the amount of die: ");
int z = console.readInt();
int[][] dice = new int[x][z];
int row = 0;
for (int i = 0; i<z; ++i){
dice[row][i] += ((int)(Math.random()*y)+1);
if ((i == z-1)&&(row!=x)) {
i = 0;
++row;
}
}
row = 0;
int[] sum = new int[x];
for (int j = 0; j<z; ++j){
sum[row]+=dice[j][row];
if ((j == z-1)&&(row!=x)) {
j = 0;
++row;
}
}
int[] counter = new int[2*y];
int k = 0;
while (k<sum.length){
for (int l = 0;l<((2*y)-1);++l){
if (sum[k]==l) ++counter[l];
if (l==((2*y)-1)) {
++k;
}
}
}
for (int m = 0;m<sum.length;++m) System.out.println(sum[m]+"'s: "+counter[m]+"times, "+((((double)counter[m])/x)*100)+"%");
}
}

first loop:
for (int i = 0; i<z; i++){
dice[row][i] += ((int)(Math.random()*y)+1);
if ((i == z-1)&&(row!=x-1)) {
i = -1;
++row;
}
}
second loop:
for (int j = 0; j<z; j++){
sum[row]+=dice[j][row];
if ((j == z-1)&&(row!=x-1)) {
j = -1;
++row;
}
}
Third loop: runs forever. I'm not sure what this is trying to achieve, so I can't fix it for you...

There are x rows but you are using z as the row loop
int[][] dice = new int[x][z]; <-- x is the row count
int row = 0;
for (int i = 0; i < z; ++i){ <--- The outer loop is iterating the rows (x),
Here's how to iterate through a 2D array
int[][] dice = new int[x][z];
for (int i = 0; i < x; i++){
for (int j = 0; j < z; j++){
// do something with dice[i][j]
}
}