CODEWITHSUNDEEP
javaarraysarraylistmultidimensional-array
Kasey
Kasey

Reputation: 41

JAVA how would I calculate the sum of each row in a 2 dimensional array?

I am writing some code to calculate the total of each row in the array. 

    public static int sum(int[][] array) {
    int total = 0;
    for (int i = 0; i < array.length; i++) {
        for (int k = 0; k < array[i].length; k++) {
            total = total + array[i][k];
        }
    }
    return total;
}

The code above is to work out the total sum for all the numbers in the two dimensional array however I am trying to work out to the total for each individual row for the array.

    public static int[] rowSums(int[][] array) {
}

I am very unsure on what to do for the code to work out the 2D array for each row.

Upvotes: 3

Views: 19504

Answers (5)

Aniket Sahrawat
Aniket Sahrawat

Reputation: 12937

If you are using Java 8 you can do it in the following way:

int[] ar = Arrays.stream(new int[][]{{1,2},{3,5}}) // source
                 .mapToInt(arr -> IntStream.of(arr).sum()) // sum inner array
                 .toArray(); // back to int[]
System.out.println(Arrays.toString(ar)); // print the array

Without stream:

int[][] arr = {{1,2},{3,5}};
// create a array that stores the total of each inner array
int[] total = new int[arr.length];
// first loop for outer array
for (int i = 0; i < arr.length; i++) {
    // loop for inner array
    for (int k = 0; k < arr[i].length; k++) {
        // since default value of total[i] is 0, we can directly use +=
        total[i] += arr[i][k];
    }
}
// print the array
System.out.println(Arrays.toString(total));

Upvotes: 4

zlakad
zlakad

Reputation: 1384

Based on @YFC_L answer, but using the enhanced loop:

public static int[] sum2(int[][] array) {

    //create an array of size based of how many rows the array has
    int[] result = new int[array.length];

    int rowIndex = 0;
    //Loop over each row
    for (int[] row : array) {
        int total = 0;

        //Calculate the sum of the row
        for (int n : row) {
            total += n;
        }

        //Store the sum in the result
        result[rowIndex++] = total;

    }
    return result;
}

Also, this method can be tested in the exatelly same way:

public static void main(String[] args) {
    System.out.println(
            Arrays.toString(sum2(new int[][]{{1, 1, 1}, {2, 2}, {3, 3}}))
    );
}

and, of course the output is the same:

[3, 4, 6]

Upvotes: 3

Mayur
Mayur

Reputation: 611

public static List<Integer> sum(int[][] array) {
    List<Integer> total = new ArrayList<>();
    for (int i = 0; i < array.length; i++) {
        int sum = 0;
        for (int k = 0; k < array[i].length; k++) {
            sum = sum + array[i][k];
        }
        total.add(sum);
    }
    return total;
}

In case if you need to use int[] after getting result,

List<Integer> total = sum(ar); 
Integer[] result = total.toArray(new Integer[0]);

Use result object for further use.

Upvotes: 1

Sasikumar Murugesan
Sasikumar Murugesan

Reputation: 4520

Try this with slight modification with your code

public static int[] sum(int[][] array) {
    List<Integer> rowTotal = new ArrayList<>();
    int total = 0;
    for (int i = 0; i < array.length; i++) {
        for (int k = 0; k < array[i].length; k++) {
            total = total + array[i][k];
        }
        rowTotal.add(total);
        total = 0;
    }
    return rowTotal.stream().mapToInt(i->i).toArray();
}

Upvotes: 1

Youcef LAIDANI
Youcef LAIDANI

Reputation: 59978

Did you mean something like this :

public static int[] sum(int[][] array) {

    //create an array of size array.length
    int[] result = new int[array.length];
    int total;

    //Loop over the first dimension 
    for (int i = 0; i < array.length; i++) {

        total = 0;//Make sure to re-initialize the total in each iteration

        //For each row calculate the sum and store it in total
        for (int k = 0; k < array[i].length; k++) {
            total += array[i][k];
        }

        //When you finish put the result of each row in result[i]
        result[i] = total;
    }
    return result;
}

Example

System.out.println(
        Arrays.toString(sum(new int[][]{{1, 1, 1}, {2, 2}, {3, 3}}))
);

Outputs

[3, 4, 6]

Upvotes: 5

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