java How to find the max of each row in a 2d array

Question

i'm writing a function that retrieves the maximum of each row in a 2d array, and returns a 1d array, where each index is relative to the 2d array's column row index.

For example, if I have an 2d array:

{1,2,3}
{4,5,6}
{7,8,9}

it should return an array of

{3,6,9}

here is my code so far:

double[] rowMaxes(double[][] nums) {
    double [] count = new double [nums.length];
    for(int i = 0; i < count.length; i++){
        for(int x = 0; x < nums[0].length; x++){
            for(int n = 0; n < nums.length; n++){
                if(nums[x][n] > count[i]){
                    count[i] = nums[x][n];
                }
            }
        }
    }
    return count;
}

Please refer to my Java 8 one liner solution

Wen-Bin Luo
– Wen-Bin Luo

2017-08-19 02:08:30 +00:00
Commented Aug 19, 2017 at 2:08 — Wen-Bin Luo
– Wen-Bin Luo, Commented Aug 19, 2017 at 2:08

Eran · Accepted Answer · 2016-04-29 12:21:57Z

1

There's no need for 3 nested loops. You only need two loops :

for(int i = 0; i < count.length; i++){
    for(int x = 0; x < nums[0].length; x++){
        if(nums[i][x] > count[i]){
            count[i] = nums[i][x];
        }
    }
}

answered Apr 29, 2016 at 12:21

Eran

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3 Comments

Randy Huang Over a year ago

the problem is that this doesn't work with negative numbers that are the max of the 2d array; only for positives

Eran Over a year ago

@RandyHuang If your array might contain negative numbers, you should initialize all the elements of the count array to Integer.MIN_VALUE

djm.im Over a year ago

@RandyHuang it missing count[i] = nums[i][0]; in the first loop

js_248 · Accepted Answer · 2016-04-29 12:48:36Z

0

You should find row and column length before going in loop. If you want to consider negative numbers then first define max as minimum negative value. You can use this

public static void main(String[] args) {
        double count[][] = {{1,2,3,8},{4,6,5,9},{0,8,9,1}};
        int r = count.length;
        int c= count[0].length;
        double out[] = new double[r];
        for(int i = 0; i < r; i++){
            double max = Integer.MIN_VALUE;
            for(int x = 0; x < c; x++){
                if(count[i][x] > max)
                    max = count[i][x];
            }
            out[i] = max;
        }
        for(int i=0;i<r;i++)
            System.out.println(out[i]);

    }

answered Apr 29, 2016 at 12:48

js_248

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Comments

Vivek Tiwari · Accepted Answer · 2017-04-25 18:24:43Z

0

public static int[] getMaxOfRow(int arr[][]){
    int grtr[]=new int[arr.length];
    grtr[0]=arr[0][0];
    for(int i=0;i<arr.length;i++){
        for(int j=0;j<arr[0].length;j++){
            if(arr[i][j]>grtr[i]){
                grtr[i]=arr[i][j];
            }
        }
    }
    return grtr;
}

answered Apr 25, 2017 at 18:24

Vivek Tiwari

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1 Comment

Rahul Sharma Over a year ago

welcome to stackflow, we strongly suggest you to read the guide (here)[stackoverflow.com/help/how-to-answer] about how to answer question.

djm.im · Accepted Answer · 2017-04-25 18:39:19Z

0

Be aware that your code will not work if all values in a row are less than zero.
When you create a new array it will be filled with the default value - it is zero.
Because it you need to add in the first loop count[i] = nums[i][0].

Something like this

double[] rowMaxes(double[][] nums) {
    double[] count = new double[nums.length];

    for (int i = 0; i < nums.length; i++) {
        count[i] = nums[i][0];
        for (int j = 1; j < nums[i].length; j++) {
            if (count[i] < nums[i][j]) {
                count[i] = nums[i][j];
            }
        }
    }

    return count;
}

If you use Java 8, you can replace inner loop with stream and max method.

for (int i = 0; i < nums.length; i++) {
    count[i] = Arrays.stream(nums[i]).max().getAsDouble();
}

edited Apr 25, 2017 at 18:39

answered Apr 25, 2017 at 18:33

djm.im

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Comments

Wen-Bin Luo · Accepted Answer · 2017-08-19 02:16:48Z

0

If you prefer to make it one line, this is the solution with any explicit looping:

Arrays.stream(nums).mapToInt((row) -> Arrays.stream(row).max().getAsInt()).max().getAsInt()

answered Aug 19, 2017 at 2:16

Wen-Bin Luo

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Comments

AdrianHHH · Accepted Answer · 2021-12-26 11:09:59Z

0

package com.vikas.array;

public class ArrayGreater_2ndApproach {

    public static void main(String[] args) {

        int d[][] = { { 1, 5, 3 }, { 4, 5, 6 }, { 7, 8, 9 } };

        for (int i = 0; i < d.length; i++) {
            int max = 0;
            for (int j = 0; j < d.length; j++) {
                if(max<d[i][j]) {
                    max = d[i][j] ;

                }
            }
            
            System.out.println("Max number in the row : " + max);
        }

    }
}

edited Dec 26, 2021 at 11:09

AdrianHHH

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answered Dec 26, 2021 at 10:54

vikas

1

2 Comments

Community Over a year ago

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.

draz Over a year ago

Please read the questions carefully. The question was about how to get the maximum per row. Also, add a comment of your solution to share your thoughts.

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