create Multi-dimensional array from single dimensional array in java

Question

I want to create a multi-dimensional array from a single dimensional array in java.

my single dimenstional array is like

  int[] grid = {5, 3, 1, 2, 0, 4, 1, 1, 3 };

I want to create a matrix of 3x3 diminsions at runtime as there are 9 elements in this array. Can anyone suggest some good idea for this. Can anyone suggest me what should I do in below code so that it can give me arraylist of 3 arrays or if someone can suggust me some better idea to perform this correctly. I know there is error in my below code.

         ArrayList<int[]> matrix = new ArrayList<>();
    int[] tempArray = new int[n];
    int j = 0;
    for(int i=0 ; i<=grid.length; i++){         

        if((i+1) / 3 == 0){         
            matrix.add(tempArray);
            j=0;
        }else{          
            tempArray[j] = grid[i];
            j++;
        }
    }

Thanks

Leaving it as a "flat" array and doing the math to transform the coordinates might be better. — Thilo
– Thilo, Commented Jun 9, 2012 at 6:54

David Webb · Accepted Answer · 2012-06-09 06:58:31Z

4

Java does multi-dimensional arrays natively; you don't need to create your own using arrays in an ArrayList.

Something like this should give you what you want:

int[] grid = {5, 3, 1, 2, 0, 4, 1, 1, 3 };
int [][] matrix = new int[3][3];

for (int x = 0; x < 3; x++) {
  for (int y = 0; y < 3; y++) {
    matrix[x][y] = grid[x + y * 3];
  }   
}

answered Jun 9, 2012 at 6:58

David Webb

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1 Comment

Stephen C Over a year ago

+1 - ArrayList<int[]> is ugly and awkward to use. (One could quibble that Java multidemensional arrays are really just arrays of arrays of ...)

Makoto · Accepted Answer · 2012-06-09 06:55:30Z

Your iteration steps too far off of the array; grid.length gives you the value 9, and the highest index is 8 - change your ending condition to be strictly less than the length.

You also don't reinitialize a new array when you're ready to put it into the ArrayList. I would suggest that, after you add the matrix, you create a new instance of tempArray:

matrix.add(tempArray);
tempArray = new int[n];
j++;

Don't reset j to 0 when you're ready to re-add some elements to your ArrayList - this puts it right back where it started. Same issue with incrementing i automatically - you'll have to be aware that i may have advanced further than you intended it to.

Lastly, I would advise on using the modulus operator instead of dividing it that way - modulo works in the same manner, and would be easier to read.

if(i % 3 == 0) { // Analogous to adding one and dividing by 3.

chaitu · Accepted Answer · 2012-06-09 07:22:09Z

public class sample {
public static void main(String args[])
  {
    int[] grid = {5, 3, 1, 2, 0, 4, 1, 1, 3 };
    int i=0,j=0;
    int count=-1;int k;
    int[][] arr=new int[3][3];

    for(i=0;i<3;i++)
    {
     count++;
      for(j=0;j<3;j++)
      {

          if(count == 0)
          {
              k=j;
              arr[i][j]=grid[k];
          }

          if(count == 1)
          {
              k=j+3;
               arr[i][j]=grid[k];
          }
          if(count == 2)
          {
              k=j+6;
               arr[i][j]=grid[k];
          }
     }

    }


   for(i=0;i<3;i++)
   {
    for(j=0;j<3;j++)
    {

        System.out.print(arr[i][j]+" ");
    }
    System.out.println(" ");
    }

  }
}

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