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Java - Sorting a 2D Array by Row Sum

Trying to write a method that swaps the rows of a 2D array in order of increasing row sum.
For example, if I have the following 2d array:
int [][] array = {4,5,6},{3,4,5},{2,3,4};
I would want it to output an array as so:
{2 3 4}, {3 4 5}, {4 5 6}
Methodology:
a.) take the sums of each row and make a 1D array of the sums
b.) do a bubble sort on rowSum array
c.) swap the rows of the original array based on the bubble sort swaps made
d.) then print the newly row sorted array.
Here's my code so far:
public void sortedArrayByRowTot() {
int [][] tempArray2 = new int [salaryArray.length [salaryArray[0].length];
for (int i = 0; i < tempArray2.length; i++) {
for (int j = 0; j < tempArray2[i].length; j++) {
tempArray2[i][j] = salaryArray[i][j];
}
}
int [] rowSums = new int [tempArray2.length];
int sum = 0;
for (int i = 0; i < tempArray2.length; i++) {
for (int j = 0; j < tempArray2[i].length; j++) {
sum += tempArray2[i][j];
}
rowSums[i] = sum;
sum = 0;
}
int temp;
int i = -1;
for(int j = rowSums.length; j > 0; j--){
boolean isSwap = false;
for (i = 1; i < j; i++) {
if(rowSums[i-1] > rowSums[i]) {
temp = rowSums[i-1];
rowSums[i-1] = rowSums[i];
rowSums[i] = temp;
isSwap = true;
}
}
if(!isSwap){
break;
}
}
for (int k = 0; k < tempArray2.length; k++) {
temp = tempArray2[i-1][k];
tempArray2[i-1][k] = tempArray2[i][k];
tempArray2[i][k] = temp;
}
for (int b = 0; b < tempArray2.length; b++) {
for (int c = 0; c < tempArray2[b].length; c++) {
System.out.print(tempArray2[b][c] + " ");
}
}
}
}
Not sure if I am doing part c of my methodology correctly?
It keeps saying "Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 2"

As #shmosel said, you can do it like this:
public static void sortedArrayByRowTot() {
int [][] array = {{4,5,6},{3,4,5},{2,3,4}};
Arrays.sort(array, Comparator.comparingInt(a -> IntStream.of(a).sum()));
}

I was able to solve my question. Thanks.
public void sortedArrayByRowTot() {
//Creates tempArray2 to copy salaryArray into
int [][] tempArray2 = new int [salaryArray.length][salaryArray[0].length];
//Copies salaryArray into tempArray2
for (int i = 0; i < salaryArray.length; i++) {
for (int j = 0; j < salaryArray[i].length; j++) {
tempArray2[i][j] = salaryArray[i][j];
}
}
//Creates rowSum array to store sum of each row
int [] rowSums = new int [tempArray2.length];
for (int i = 0; i < tempArray2.length; i++) {
for (int j = 0; j < tempArray2[0].length; j++) {
rowSums[i] += tempArray2[i][j];
}
}
//Modified Bubble Sort of rowSum array (highest to lowest values)
int temp;
int i = 0;
for(int j = rowSums.length; j > 0; j--){
boolean isSwap = false;
for (i = 1; i < j; i++) {
if(rowSums[i-1] < rowSums[i]) {
temp = rowSums[i-1];
rowSums[i-1] = rowSums[i];
rowSums[i] = temp;
isSwap = true;
//swaps rows in corresponding tempArray2
int [] temp2 = tempArray2[i-1];
tempArray2[i-1] = tempArray2[i];
tempArray2[i] = temp2;
}
}
if(!isSwap){
break;
}
}
//Prints sorted array
System.out.println("Sorted array: ");
for (i = 0; i < tempArray2.length; i++) {
for (int j = 0; j < tempArray2[i].length; j++) {
System.out.print("$"+ tempArray2[i][j] + " ");
}
System.out.println();
}
}

You may try this way. That I have solved.
public class Solution{
public static void sortedArrayByRowTot() {
int [][] salaryArray = { {4,5,6},{3,4,5},{2,3,4} };
int [][] tempArray2 = new int [salaryArray.length][salaryArray[0].length];
for (int i = 0; i < salaryArray.length; i++) {
for (int j = 0; j < salaryArray[i].length; j++) {
tempArray2[i][j] = salaryArray[i][j];
}
}
// Buble Sort to store rowSums
int [] rowSums = new int [tempArray2.length];
for (int i = 0; i < tempArray2.length; i++) {
for (int j = 0; j < tempArray2[0].length; j++) {
rowSums[i] += tempArray2[i][j];
}
}
//Buble Sort by Rows Sum (Lowest Value to Highest)
int temp;
int i = 0;
for(int j = rowSums.length; j > 0; j--){
boolean isSwap = false;
for (i = 1; i < j; i++) {
if(rowSums[i-1] > rowSums[i]) {
temp = rowSums[i-1];
rowSums[i-1] = rowSums[i];
rowSums[i] = temp;
isSwap = true;
//swaps rows in corresponding tempArray2
int [] temp2 = tempArray2[i-1];
tempArray2[i-1] = tempArray2[i];
tempArray2[i] = temp2;
}
}
if(!isSwap){
break;
}
}
/** No Need.
for (int k = 0; k < tempArray2.length; k++) {
temp = tempArray2[i-1][k];
tempArray2[i-1][k] = tempArray2[i][k];
tempArray2[i][k] = temp;
}
*/
for (int b = 0; b < tempArray2.length; b++) {
for (int c = 0; c < tempArray2[b].length; c++) {
System.out.print(tempArray2[b][c] + " ");
}
}
}
public static void main(String[] args) {
sortedArrayByRowTot();
}
}

How do I reverse a boolean array in java?

I want to reverse a boolean array. free is the array. Here's my code:
public boolean[][] free = new boolean[6][6];
free = !free;
I get an error saying the operator ! is undefined. What should I do?
EDIT
It is not empty. I just want to inverse the values.
public boolean[][] free = new boolean[6][6];
void initFree(State s) {
for (int i = 0; i < nbcars; i++){
if (horiz[i]){
for (int j = 0; j < (len[i]-1); j++)
free[moveon[i]][s.pos[i]+j]=true;
}
if (!horiz[i]){
for (int j = 0; j < (len[i]-1); j++)
free[s.pos[i]+j][moveon[i]]=true;
}
}
free = !free;
}

You get operator ! is undefined simply because Java doesn't define ! operator on a two dimensional boolean array.
One way you could achieve what you want is by iterating over each value and then use the ! operator.
for(int i=0; i<free.length; i++)
{
for(int j=0; j<free[i].length; j++)
{
free[i][j] != free[i][j];
}
}

Here's a simple example you can modify for your uses. I included an invert method.
public class StackOverflowExample {
public static void main(String[] args) {
int ROW = 10, COL = 10;
boolean[][] ATwoDBoolArray = new boolean[ROW][COL];
PutValuesInArray(ATwoDBoolArray);
printArray(ATwoDBoolArray);
invertArray(ATwoDBoolArray);
printArray(ATwoDBoolArray);
}
private static boolean[][] PutValuesInArray(boolean array[][]) {
for (int i = 0; i < array.length; i++) {
for (int j = 0; j < array[i].length; j++) {
array[i][j] = false;
}
}
return array;
}
private static void printArray(boolean[][] array){
for (int i = 0; i < array.length; i++) {
for (int j = 0; j < array[i].length; j++) {
System.out.println(array[i][j]);
}
}
}
private static boolean[][] invertArray(boolean array[][]){
for (int i = 0; i < array.length; i++) {
for (int j = 0; j < array[i].length; j++) {
if(array[i][j]){
array[i][j] = false;
}else{
array[i][j] = true;
}
}
}
return array;
}
}

This method inverts all the values in a given 2-dimensional boolean array.
static void invertBooleanArray(boolean[][] arr) {
for (int i = 0; i < arr.length; i++)
for (int j = 0; j < arr[0].length; j++)
arr[i][j] = !arr[i][j];
}

My matrix doesn’t change when I try to perform scalar multiplication

we're supposed to multiply every element in the matrix by a number, in this case "k". not sure what i'm doing wrong but it wont work. HELP! i have edited and added the whole project so far.
public class Matrix {
private int r;//rows
private int c;//columns
private int[][] neo; //2D array
public static void main(String[] args) {
Matrix m1 = new Matrix(3,4);
Matrix m2 = new Matrix(3,4);
System.out.println(m2);
try {
Matrix m3 = m1.multiply(m2);
} catch (Exception e) {
e.printStackTrace();
}
m2.scaleMult(k);
}//main
public Matrix(int row, int column) {
r = row;
c = column;
neo = new int[r][c];
for(int i = 0; i < neo.length; i++) {
for (int j = 0; j < neo[i].length; j++) {
neo[i][j] = (int) (1 + Math.random() * 100);
}//forLoop
}//forLoop
System.out.println(Arrays.toString(neo));
}//Matrix
public Matrix copyMatrix(Matrix m) {
Matrix copy = new Matrix(m.r, m.c);
for (int i = 0; i < r; i++) {
System.arraycopy(this.neo[i], 0, copy.neo[i], 0, this.neo[i].length);
}//forLoop
return copy;
}//copyMatrix
public void scaleMult(int k){
for (int i = 0; i < r; i++)
for (int j = 0; j < c; j++)
this.neo[i][j] * k;
}//scaleMult
public boolean equals(Matrix m2) {
if (this.r != m2.r || this.c != m2.c) {
return false;
}
for (int i = 0; i < r; i++) {
for (int j = 0; j < c; j++) {
if (this.neo[i][j] != m2.neo[i][j]) {
return false;
}
}
}
return true;
}//equalsMethod
public Matrix multiply(Matrix m2) throws Exception {
if (this.c != m2.r) {
throw new RuntimeException();
}//if
Matrix m3 = new Matrix(this.r, m2.c);
for (int i = 0; i < this.r; i++) {
for (int j = 0; j < m2.c; j++) {
m3.neo[i][j] = 0;
for (int k = 0; k < this.c; k++) {
m3.neo[i][j] += this.neo[i][k] * m2.neo[k][j];
}//forK
}//forJ
}//forI
return m3;
}//multiplyMethod
}//class

Change your scaleMult method to this and it should work:
public void scaleMult(int k) {
for (int i = 0; i < r; i++) {
for (int j = 0; j < c; j++) {
this.neo[i][j] *= k;
// you forgot to assign the value, basically we multiply neo[i][j] by k and make neo[i][j] receive that value
// making this.neo[i][j] = this.neo[i][j] *k; would work as well
}
}
}//scaleMult
Also, based on the example you provided on your main method, your code will launch an exception on the multiply method, because as you specified, you can only multiply two matrixes if one's columns amount is equal to the other's row amount. Other than that, I would advise on creating a new class just for your main method.

If your question is multiply a matrix by a number, then here is a very simple example.
public static void main(String []args){
int[][] a = {{1,2,3},{4,5,6}};
int[][] b=new int[2][3];
int i,j,k=2;
for(i=0;i<2;i++)
for(j=0;j<3;j++)
b[i][j]=a[i][j]*k;
for(i=0;i<2;i++)
for(j=0;j<3;j++)
System.out.println(b[i][j]);
}
There must be some array variable on left which should be assigned the multiplied value.
Do this helped? If not, please post your complete code.

Why can't i generate this 10x10 2D array?

I am trying to generate this 2D Array maze 10 by 10 with numbers 0-9 in each row for 10 rows, but I keep getting array out of bounds exception. I double checked my indexes and the loop format and everything looks standard.
public class MazeDemo {
public static void main(String[] args) {
Maze maze = new Maze(10, 10);
maze.generate();
}
}
class Maze {
int N, M;
int[][] cell = new int[N][M];
public Maze(int N, int M) {
this.N = N;
this.M = M;
}
public void generate() {
for (int i = 0; i < N; i++) {
int counter = 0;
for (int j = 0; i < M; j++) {
cell[i][j] = counter;
counter++;
}
}
display(cell, 10, 10);
}
public static void display(int a[][], int N, int M) {
for (int i = 0; i < N; i++) {
for (int j = 0; j < M; j++) {
System.out.print(a[i][j]);
}
}
}
}
What is going on here? Why am I getting the out of bounds exception?

When you declare cell, N and M are 0. Change it to something like
int N, M;
int[][] cell;
public Maze(int N, int M) {
this.N = N;
this.M = M;
this.cell = new int[N][M]; // <-- add this.
}
And in generate, this
for (int j = 0; i < M; j++) {
should be
for (int j = 0; j < M; j++) {

The problem is in the generate method in:
for (int j = 0; i < M; j++)
^
it should be:
for (int j = 0; j < M; j++)

transpose double[][] matrix with a java function?

Do anybody have a function with which I can transpose a Matrix in Java which has the following form:
double[][]
I have function like this:
public static double[][] transposeMatrix(double [][] m){
for (int i = 0; i < m.length; i++) {
for (int j = i+1; j < m[0].length; j++) {
double temp = m[i][j];
m[i][j] = m[j][i];
m[j][i] = temp;
}
}
return m;
}
but its wrong somewhere.

public static double[][] transposeMatrix(double [][] m){
double[][] temp = new double[m[0].length][m.length];
for (int i = 0; i < m.length; i++)
for (int j = 0; j < m[0].length; j++)
temp[j][i] = m[i][j];
return temp;
}

If you would like to use an external library, Apache Commons Math provides the utility to transpose a matrix. Please refer to it official site.
First, you have to create a double array double[][] arr, as you have already done. Then, the transposed 2d matrix can be achieved like this
MatrixUtils.createRealMatrix(arr).transpose().getData()

Since Java 8, you can do this:
public static double[][] transposeMatrix(final double[][] matrix) {
return IntStream.range(0, matrix[0].length)
.mapToObj(i -> Stream.of(matrix).mapToDouble(row -> row[i]).toArray())
.toArray(double[][]::new);
}

Java Class to Transpose a matrix :-
import java.util.Scanner;
public class Transpose {
/**
* #param args
*/
static int col;
static int row;
static int[][] trans_arr = new int[col][row];
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner sc = new Scanner(System.in);
int m = sc.nextInt();
col = m;
int n = sc.nextInt();
row = n;
int[][] arr = new int[row][col];
for (int i = 0; i < row; i++) {
for (int j = 0; j < col; j++) {
arr[i][j] = sc.nextInt();
System.out.print(arr[i][j] + " ");
}
System.out.println();
}
int[][] trans_arr = new int[col][row];
for (int i = 0; i < row; i++) {
for (int j = 0; j < col; j++) {
trans_arr[j][i] = arr[i][j];
}
}
for (int i = 0; i < col; i++) {
for (int j = 0; j < row; j++) {
System.out.print(trans_arr[i][j] + " ");
}
System.out.println();
}
}
}

Here is the method
public static double[][] transpose(double arr[][]){
int m = arr.length;
int n = arr[0].length;
double ret[][] = new double[n][m];
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
ret[j][i] = arr[i][j];
}
}
return ret;
}

Here is a code to transpose a two dimensional matrix "In Place" (not using another data structure to save output) and hence is more memory efficient:
Same below algorithm can be used for int or char or string data types as well.
public static double[][] transposeDoubleMatrix(double[][] matrix) {
int n = matrix.length;
for (int i = 0; i < n; i++) {
for (int j = i; j < n; j++) {
double tmp = matrix[j][i];
matrix[j][i] = matrix[i][j];
matrix[i][j] = tmp;
}
}
return matrix;
}

Here's a small change!
for (int j = i; j < m[0].length; j++)