java: adding one value to one column in a 2D-array

Question

I have a 2D-array to which I have to add a certain value, but only to one column of the 2D-array. One row of the 2D-array has to skipted and will stay the same as before.

I already have a code (see below), but that is just adding the value, not calculating it.

My code so far:

double lowest = Double.parseDouble(excelMatrix[0][0]);
    int row = 0, column = 0;
    List usedRow = new ArrayList(); 
    for(int r = 0; r<excelMatrix.length-1; r++){

        for(int c = 0; c<excelMatrix[r].length; c++){
            double number = Double.parseDouble(excelMatrix[r][c]);
            if(lowest > number) {
                lowest = number;
                row = r;
                column = c;
            }                   
        }                       
    }                       
    usedRow.add(row);

for(int r = 0; r < excelMatrix.length; r++){
   if( r != row)
   excelMatrix[r][column] += lowest;
}

The initial matrix looks something like this:

{1 , 2 , 3 , 4 , 5}  
{5 , 4 , 3 , 2 , 1}  
{4 , 5 , 1 , 2 , 3}  
{2 , 3 , 4 , 5 , 1}     
{3 , 4 , 5 , 1 , 2}

and by adding 10 to column 3, except row 3, I would like to get:

{1 , 2 , 3 , 14 , 5}  
{5 , 4 , 3 , 12 , 1}  
{4 , 5 , 1 , 12 , 3}  
{2 , 3 , 4 , 5 , 1}  
{3 , 4 , 5 , 11 , 2}

But at the moment I am getting:

{1 , 2 , 3 , 410 , 5}  
{5 , 4 , 3 , 210 , 1}  
{4 , 5 , 1 , 210 , 3}  
{2 , 3 , 4 , 5 , 1}  
{3 , 4 , 5 , 110 , 2}

I hope the example makes my problem clear. Thank you!

In what way is the output you need different than the output you currently get? — Eran
– Eran, Commented Aug 14, 2016 at 10:39
@Eran I just updated the question. I hope now it is clear what my problem is. It is just adding the value but not calculating it. — boersencrack
– boersencrack, Commented Aug 14, 2016 at 10:45
@boersencrack it looks like you are appending strings. How does excelMatrix look like — Samuel Toh
– Samuel Toh, Commented Aug 14, 2016 at 10:47
What are you trying to calculate with it? It might be useful to post more of the code, i.e. the method where you're meant to calculate using the data. — Matt
– Matt, Commented Aug 14, 2016 at 10:47

Eran · Accepted Answer · 2016-08-14 10:49:24Z

1

Based on the output you are getting, it looks like the type of excelMatrix is String[][], so when you are using the += operator you are concatenating a number to a String.

If you change your excelMatrix array to int[][], you'll get the desired output.

If excelMatrix must remain a String[][], you can still perform the addition by converting the String to int, performing addition and converting back to String (though that would be less efficient) :

excelMatrix[r][column] = Integer.toString(Integer.parseInt(excelMatrix[r][column]) + value);

answered Aug 14, 2016 at 10:49

Eran

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Sakalya · Accepted Answer · 2016-08-14 10:54:07Z

0

This code snippet will solve your problem.

for(int i =0;i<numOfRows;i++) {
    for(int j= 0;j<numOfColumns;j++) {
       if(i != rowToBeSkipped) {
         excelMatrix[i][j] = excelMatrix[i][j] + value;
        }
    }
}

answered Aug 14, 2016 at 10:54

Sakalya

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