Trying to transpose an array, but getting array out of bounds

Question

I am trying to convert a 2D array. The content of a horizontal row is transferred to vertical column.

public static void change(short image[])
{

   int arrayLength = 29; // row length
   int arrayWidth = 10; // column length
   // array with values
   short[][] decompressedImage = new short[arrayLength][arrayWidth]; 

   // array to store transposed image
   short[][] transposedImage = new short[arrayWidth][arrayLength];

   // store transposed values

   for (int i=0;i<arrayWidth; i++){
      for (int j=0;j<arrayLength; j++){
         transposedImage[j][i]=decompressedImage[i][j];
      }
   }
}

Answer 1

Here's an example of how the rotation works, the rotation is really only the middle for loop,(below the comment), I also made it for both directions with output:

    String[][] matrix = {{"A","B","C"},{"D","E","F"},{"G","H","I"}};
String[][] tmp = new String[matrix.length][matrix.length];

    //PRINT BEFORE ROTATION
for(int row=0; row<matrix.length;row++){
    for(int col=0; col<matrix.length;col++){
        System.out.print(matrix[row][col] + "  ");
    }
    System.out.println();
}

    //HERE IS THE ROTATION
for(int row=0; row<matrix.length;row++){
    for(int col=matrix.length-1; col>=0;col--){
        tmp[col][row] = matrix[row][matrix.length-1-col];
    }
}

    //PRINT AFTER ROTATION
System.out.println("Rotated");
for(int row=0; row<matrix.length;row++){
    for(int col=0; col<matrix.length;col++){
        System.out.print(tmp[row][col] + "  ");
    }
    System.out.println();
}

OUTPUT:

A  B  C  
D  E  F  
G  H  I  

Rotated

C  F  I  
B  E  H   
A  D  G  

And if you want to rotate it the second way.

replace the for loop of : //HERE IS THE ROTATION

by this:

    for(int row=matrix.length-1; row >= 0; row--){
    for(int col=0; col<matrix.length;col++){
        tmp[col][row] = matrix[matrix.length-1-row][col];
    }
}

OUTPUT:

A  B  C  
D  E  F  
G  H  I  

Rotated

G  D  A  
H  E  B  
I  F  C  

Answer 2

if lowLength is 29, you only can access to 28. because index of for starts from 0.

change

i < arrayWidth --> i < arrayWidth - 1
i < arrayLength --> i < arrayLength - 1

It is just a possibility.

Answer 3

Change below line :

 short[][] transposedImage = new short[arrayLength][arrayWidth];  

instead of

short[][] transposedImage = new short[arrayWidth][arrayLength];  

This is your code after change :

int arrayLength = 29; // row length
int arrayWidth = 10; // column length
short[][] transposedImage = new short[arrayLength][arrayWidth];
short[][] decompressedImage = new short[arrayWidth][arrayLength];

// store transposed values
for (int i=0;i<arrayWidth; i++){
  for (int j=0;j<arrayLength; j++){
     transposedImage[j][i]=decompressedImage[i][j];
  }
}

Answer 4

Assuming arrayLength & arrayWidth to be the length & width of decompressedImage , the loop construct

for (int i=0;i<arrayWidth; i++){
  for (int j=0;j<arrayLength; j++){
     transposedImage[j][i]=decompressedImage[i][j];
  }
}

is actually in accordance with the dimensions of transposedImage and NOT of decompressedImage ie your loop variables i & j take the dimensions of transposedImage.

Thus change the statement

 transposedImage[j][i]=decompressedImage[i][j];

to

transposedImage[i][j]=decompressedImage[j][i];

I guess that should help.

Answer 5

you defined the arre transposedImage of dimension [arrayWidth][arrayLength] but, while you are accessing the array, you are looping until [arrayLength][arrayWidth] , notice the i and j loop of yours. according the loop, it should be,

transposedImage[i][j]=decompressedImage[j][i];

and NOT

transposedImage[j][i]=decompressedImage[i][j];

corrected code segment,

short[][] decompressedImage = new short[arrayLength][arrayWidth];
short[][] transposedImage = new short[arrayWidth][arrayLength];
for (int i=0;i<arrayWidth; i++){
  for (int j=0;j<arrayLength; j++){
     transposedImage[i][j]=decompressedImage[j][i];
  }
}