How to write a program to calculate and display sum in two dimensional array?

[Javanoobs]

I have a college tutorial question that required me to write a program which need to calculate and display the sum of each column of a two dimensional array. For example, in the following array

2 6 -1 5
8 2 7 -5
1 0 4 4

the method shoudl display the following
The sum of column 0 is 11
The sum of column 1 is 8
The sum of column 2 is 10
The sum of column 3 is 4

Assume that in the calling program the array A is declared as float A[MAXROW][MAXCOL]; where MAXROW and MAXCOL are global int constants.

The method should have a two dimensional array as its only parameter and shold not return any values.

I have roughly wrote something on a paper, but i jst dun get the idea how to link all the tings 2gether, can anyone pls help me of this?

public class array
public static final MAXROW{
public static final MAXCOL{

public void calculate Sum(){
float A[MAXROW][MAXCOL];
for (int i = 0; i<MAXROW.length; i++)
{
for (int j = 0; j<MAXCOL.length;j++)
{
(I don't have idea in tis part)
}
}

i knw my code is poor and not completed, but im in the progress of learning, im using netbean 6.9.1, pls help me out ..thx

[JosAH]

Do it 'bottom up'; i.e. calculate the sum of one column; let j be the column for which you have to add all the numbers of a two dimensional array 'a'. The number of rows is known, i.e. a.length, so finding that total is just one loop:

int sum= 0;
for (int row= 0; row < a.length; a++)
   sum+= a[row][j];

All you have to do is apply the above code snippet to all columns of the array and add a few System.out.println( ... ) statements.

kind regards,

Jos

[Javanoobs]

may i knw y it ask me to declared the [maxrow][maxcol] and declared it as global int? if lik u say apply 1 loop, and how to deal wit tis maxrow and maxcol?

[Javanoobs]

and also do i need to cr8 a new class for calculating the array? or do it in the main?

[JosAH]

may i knw y it ask me to declared the [maxrow][maxcol] and declared it as global int? if lik u say apply 1 loop, and how to deal wit tis maxrow and maxcol?
and also do i need to cr8 a new class for calculating the array? or do it in the main?

If you want to ask me a question please use (more or less) proper English; I also reply in (more or less) proper English.

kind regards,

Jos

[sunde887]

Im having a hard time understanding your questions, but I think the easiest way to do this would be to create a static method to produce the sum of a single array, then loop through the 2d array applying the static method and storing the values in a new array.

[Javanoobs]

If you want to ask me a question please use (more or less) proper English; I also reply in (more or less) proper English.

kind regards,

Jos

my apologize...because I am having hard time to understand your explanation, Im stil a beginner in this, so hope you could explain this in details, you help will be fully appreciated...

[Javanoobs]

Im having a hard time understanding your questions, but I think the easiest way to do this would be to create a static method to produce the sum of a single array, then loop through the 2d array applying the static method and storing the values in a new array.

ok...can you provide some coding example so I can get exactly what you said? your help will be kindly appreciated...:)

[sunde887]

How would you find the sum of a single array? Each index in a 2d array is actually a single array

int[][] x = new int[4][];
int[0] = { 1, 2, 3 };
int[1] = { 4, 5, 2 };
int[2] = { 6, 8, 9 };
int[3] = { 2, 5, 9 , 10 };

is a 2d array, so it simply comes down to finding the sum of a single array then applying that process to each element of a 2d array.

[JosAH]

my apologize...because I am having hard time to understand your explanation, Im stil a beginner in this, so hope you could explain this in details, you help will be fully appreciated...

As I wrote you should apply my code snippet to a single column j of your matrix. It would be easiest to turn it into a little method, like this:

private void calculateColumn(int[][] array, int j) {
   // my code snippet goes here
   // and a System.out.println( ... ) statement goed here
}

If you want to print the results of all columns you should apply the method above to each and every column of your matrix, like this:

public void calculate(int[][] array) {
   for (int col= 0; col < array[0].length; col++)
      calculateColumn(array, col);
}

That's all the code it takes ...

kind regards,

Jos

[Petr]

generic, anonymously class, interface )

import java.util.ArrayList;
import java.util.List;

public class SumEx {
    public static void main(String[] arg) {
        Integer[][] mass = {
                {2, 6, -1, 5},
                {8, 2, 7, -5},
                {1, 0, 4, 4},
        };
        System.out.println("Summ column 0 : " + summ(build(mass, 0)));
        System.out.println("Summ column 1 : " + summ(build(mass, 1)));
        System.out.println("Summ column 2 : " + summ(build(mass, 2)));
        System.out.println("Summ column 3 : " + summ(build(mass, 3)));
    }

    private static <T extends Number> List<T> build(T[][] mass, int index) {
        List<T> list = new ArrayList<T>();
        for (T[] t : mass) {
            list.add(t[index]);
        }
        return list;
    }

    private static <T extends Number> double summ(List<T> list) {
        return forEach(list, new Operation<Number>() {
            @Override
            public Number invoke(Number result, Number number) {
                return result.doubleValue() + number.doubleValue();
            }
        });
    }

    interface Operation<A extends Number> {
        public A invoke(A result, A a);
    }

    private static <T extends Number> double forEach(List<T> list, Operation<Number> operation) {
        double result = 0D;
        for (T t : list) {
            result = operation.invoke(result, t).doubleValue();
        }
        return result;
    }
}

[Javanoobs]

thanks to josah and sunde...i know how it goes along now...thanks you guys help, and sorry for disturbing you both...peace =)

[Javanoobs]

generic, anonymously class, interface )

import java.util.ArrayList;
import java.util.List;

public class SumEx {
    public static void main(String[] arg) {
        Integer[][] mass = {
                {2, 6, -1, 5},
                {8, 2, 7, -5},
                {1, 0, 4, 4},
        };
        System.out.println("Summ column 0 : " + summ(build(mass, 0)));
        System.out.println("Summ column 1 : " + summ(build(mass, 1)));
        System.out.println("Summ column 2 : " + summ(build(mass, 2)));
        System.out.println("Summ column 3 : " + summ(build(mass, 3)));
    }

    private static <T extends Number> List<T> build(T[][] mass, int index) {
        List<T> list = new ArrayList<T>();
        for (T[] t : mass) {
            list.add(t[index]);
        }
        return list;
    }

    private static <T extends Number> double summ(List<T> list) {
        return forEach(list, new Operation<Number>() {
            @Override
            public Number invoke(Number result, Number number) {
                return result.doubleValue() + number.doubleValue();
            }
        });
    }

    interface Operation<A extends Number> {
        public A invoke(A result, A a);
    }

    private static <T extends Number> double forEach(List<T> list, Operation<Number> operation) {
        double result = 0D;
        for (T t : list) {
            result = operation.invoke(result, t).doubleValue();
        }
        return result;
    }
}

once again, thanks to you peter for your help, but do i need to do so much abstract coding? I mean this is just a simple array calculation program, just my opinion...hope to seek your advice...