calculate the minimum value for each column in 2D array

Question

I have a 2D array , iam trying to calculate the minimum value for each column and put the result in the result array.

the code bellow is calculating the minimum value for each row , how can i get the min value for each column.

        import java.util.*;

         class Test20 {

        public static void main ( String [] args) {


            int[][] array = {{6,3,9},
                             {0,8,2},
                             {3,7,5}};



           Test20 test = new Test20();

        System.out.print(Arrays.toString(test.mincol(array)));
      }

     public static int[] mincol (int[][] n) {
    int[] result = new int[n.length];

    for (int i = 0; i < n.length; i++) {

        int min = n[0][i];

        for (int j = 0; j < n[0].length; j++) {

            if (n[j][i] < min) {
                min = n[j][i];
            }
        }
        result[i] = min;
    }
    return result;
     }
   }

Answer 1

Just change the loop the following way:

min = 0;
for(int i=0;i<n.length;i++){
     for(int j=0;j<n[0].length;j++){
        if(n[j][i]<n[j][min]){
        min=j;
}
result[i]=n[min][i];
}

Be aware that you instantiate your result array by the length of the first dimension in your array but later use the n[][] param for looping and access the length of the second dimension in your loop.

If your two dim array is for example 4x5, this will cause ArrayOutOfBoundsExceptions.

Answer 2

Your for loop looks ok. Check the code below I fixed some minor issues.

Based on your code replace Class code with below:

public class Test {
public static void main(String[] args) {
    int[][]array={{6,1,9}, {0,1,2}, {3,7,5}};
    int[] test;

    test = minrow(array);
    for(int i=0; i<test.length; i++){
        System.out.println(test[i]);
    }
}
public static int[] minrow(int[][] n){

    int [] result = new int[n.length];
    int min;

    for(int i=0;i<n.length;i++){
        min=0;
        for(int j=0;j<n[i].length;j++){
            if(n[i][j]<n[i][min]){
                min=j;
            }
        }
        result[i]=n[i][min];
    }
    return result;
}
}

Answer 3

You only need to do the same thing but inverting the variables

for(int i=0;i<n.length;i++){
   for(int j=0;j<n[0].length;j++){
       if(n[j][i]<n[min][j]){
           min=i;
       }
       result[j]=n[min][j];
    }

}

Answer 4

If your code is correct just change:

if(n[i][j]<n[i][min]){
            min=j;
}

with

if(n[i][j]<n[result[i]][j]){
            result[i]=i;
}

finally

for(int i=0;i<n.length;i++) result[i]=n[result[i][j];

you don't need min . But change

 int [] result = new int[n.length];

to

int [] result = new int[n[0].length];

Answer 5

How about you transpose your two dimensional array like:

     public static int[][] transpose (int[][] original) {
        int[][] array = new int[original.length][];
        // transpose
        if (original.length > 0) {
            for (int i = 0; i < original[0].length; i++) {
                array[i] = new int[original[i].length];
                for (int j = 0; j < original.length; j++) {
                    array[i][j] = original[j][i];
                }
            }
        }
        return array;
    }

and then call it as:

System.out.print(Arrays.toString(test.minrow(transpose(array))));

Or, if you want to go without transpose, this is how you can do:

    public static int[] mincol (int[][] n) {
        int[] result = new int[n.length];
        for (int i = 0; i < n.length; i++) {
            int min = n[0][i];
            for (int j = 0; j < n[0].length; j++) {
                if (n[j][i] < min) {
                    min = n[j][i];
                }
            }
            result[i] = min;
        }
        return result;
    }