Convert 3D array to 2D array in Java-CodePudding

I have a 3D int array named "array[9][3][3]" and I want to convert it into a 2D array "arrayConvt[9][9]". Do not imagine "array[9][3][3]" as a 3D object, but rather a 2D object that has 9 rows and just 1 column and each cell is further divided into a 3X3 2D array. What I want to do is get the content of the first 3 cells and add them side by side to make a 2X8 2D array. Then the next 3 cells (4-6) and add them 1 line below in 2D array to fill 5X8 contents. Then the last 3 cells from the 3D array to the last rows of the 2D array (8X8 cells of the 2D array). The crux of what I have been describing.

CodePudding user response：

Try this.

public static void main(String[] args) {
    int[][][] array = {
        {{0, 1, 2}, {3, 4, 5}, {6, 7, 8}},
        {{10, 11, 12}, {13, 14, 15}, {16, 17, 18}},
        {{20, 21, 22}, {23, 24, 25}, {26, 27, 28}},
        {{30, 31, 32}, {33, 34, 35}, {36, 37, 38}},
        {{40, 41, 42}, {43, 44, 45}, {46, 47, 48}},
        {{50, 51, 52}, {53, 54, 55}, {56, 57, 58}},
        {{60, 61, 62}, {63, 64, 65}, {66, 67, 68}},
        {{70, 71, 72}, {73, 74, 75}, {76, 77, 78}},
        {{80, 81, 82}, {83, 84, 85}, {86, 87, 88}},
    };
    int[][] arrayConv = new int[9][9];

    int[][] s = {
        {0, 0}, {0, 3}, {0, 6},
        {3, 0}, {3, 3}, {3, 6},
        {6, 0}, {6, 3}, {6, 6},
    };

    for (int i = 0, p = 0; i < 9;   i,   p)
        for (int j = 0, r = s[p][0]; j < 3;   j,   r)
            for (int k = 0, c = s[p][1]; k < 3;   k,   c)
                arrayConv[r][c] = array[i][j][k];

    for (int[] r : arrayConv)
        System.out.println(Arrays.toString(r));
}

output:

[0, 1, 2, 10, 11, 12, 20, 21, 22]
[3, 4, 5, 13, 14, 15, 23, 24, 25]
[6, 7, 8, 16, 17, 18, 26, 27, 28]
[30, 31, 32, 40, 41, 42, 50, 51, 52]
[33, 34, 35, 43, 44, 45, 53, 54, 55]
[36, 37, 38, 46, 47, 48, 56, 57, 58]
[60, 61, 62, 70, 71, 72, 80, 81, 82]
[63, 64, 65, 73, 74, 75, 83, 84, 85]
[66, 67, 68, 76, 77, 78, 86, 87, 88]

CodePudding user response：

First, construct some source data

int src[][][] = new int[9][3][3];
for (int r = 0; r < 9; r  ) {
    for (int rr = 0; rr < 3; rr  ) {
        for (int cc = 0; cc < 3; cc  ) {
            src[r][rr][cc] = r * 9   rr * 3   cc   1;
        }
    }
}
for (int[][] d : src) {
    System.out.println(Arrays.deepToString(d));
}

prints

[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
[[10, 11, 12], [13, 14, 15], [16, 17, 18]]
[[19, 20, 21], [22, 23, 24], [25, 26, 27]]
[[28, 29, 30], [31, 32, 33], [34, 35, 36]]
[[37, 38, 39], [40, 41, 42], [43, 44, 45]]
[[46, 47, 48], [49, 50, 51], [52, 53, 54]]
[[55, 56, 57], [58, 59, 60], [61, 62, 63]]
[[64, 65, 66], [67, 68, 69], [70, 71, 72]]
[[73, 74, 75], [76, 77, 78], [79, 80, 81]]

Now transform the matrix

int[][] dst = transform(src);

for (int[] row : dst) {
    System.out.println(Arrays.toString(row));
}

prints

[1, 2, 3, 10, 11, 12, 19, 20, 21]
[4, 5, 6, 13, 14, 15, 22, 23, 24]
[7, 8, 9, 16, 17, 18, 25, 26, 27]
[28, 29, 30, 37, 38, 39, 46, 47, 48]
[31, 32, 33, 40, 41, 42, 49, 50, 51]
[34, 35, 36, 43, 44, 45, 52, 53, 54]
[55, 56, 57, 64, 65, 66, 73, 74, 75]
[58, 59, 60, 67, 68, 69, 76, 77, 78]
[61, 62, 63, 70, 71, 72, 79, 80, 81]

sr,sc - the source row and column of the inner 3x3 matrix to copy
r - the destination row to contain the above
the outer loop is used to create the destination row as well as allow
intermediate increments of key variables
and the JavaDoc explains System.arraycopy

public static int[][] transform(int[][][] src) {
  int sr = 0;
  int[][] dst = new int[9][9];
  for (int x = 0; x < 3; x  ) {
     for (int sc = 0; sc < 3; sc  ) {
        int r = x * 3   sc;
        System.arraycopy(src[sr][sc], 0, dst[r], 0, 3);
        System.arraycopy(src[sr   1][sc], 0, dst[r], 3, 3);
        System.arraycopy(src[sr   2][sc], 0, dst[r], 6, 3);
     }
     sr = sr   3;
  }
  return dst;
}