将2D数组的列拆分为一个单独的2D数组。

huangapple
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英文:

Splitting columns of 2D array into a separate 2D array

问题

I would like to send certain columns of a 2D array to another method as a 2D array. For example, I have the following array:

  1. 1 2 6 4
  2. 2 5 3 9
  3. 2 5 1 3

I would like to send, let's say, the middle 2 columns to a method as the 2D array:

  1. 2 6
  2. 5 3
  3. 5 1
英文:

I would like to send certain columns of a 2D array to another method as a 2D array. For example, I have the following array:

  1. 1 2 6 4
  2. 2 5 3 9
  3. 2 5 1 3

I would like to send lets say the middle 2 columns to a method as the 2D array:

  1. 2 6
  2. 5 3
  3. 5 1

How would I split this in a way that I could clarify the amount of columns being split and where I want the split to start and end. My understanding is that System.arrayCopy() would be an efficient way of performing this, however, I can only copy a 1D array with it.

答案1

得分: 2

尝试这个。

  1. int[][] arr = new int[][]{
  2.         {1, 2, 6, 4},
  3.         {2, 5, 3, 9},
  4.         {2, 5, 1, 3}
  5. };
  7. int startColumn = 1;
  8. int endColumn = 2;
  9. int[][] result = Arrays.stream(arr)
  10.         .map(row -> IntStream.rangeClosed(startColumn, endColumn)
  11.                 .map(j -> row[j]).toArray())
  12.         .toArray(int[][]::new);
  14. System.out.println(Arrays.deepToString(res));

输出: [[2, 6], [5, 3], [5, 1]]

它对二维数组进行流处理，对于每一行，它通过选择从 startColumn 到 endColumn（包括边界列）的列来构建一个一维数组，并将每个数组收集到一个二维数组中。

英文:

Try this.

  1. int[][] arr = new int[][]{
  2.         {1, 2, 6, 4},
  3.         {2, 5, 3, 9},
  4.         {2, 5, 1, 3}
  5. };
  7. int startColumn = 1;
  8. int endColumn = 2;
  9. int[][] result = Arrays.stream(arr)
  10.         .map(row -> IntStream.rangeClosed(startColumn, endColumn)
  11.                 .map(j -> row[j]).toArray())
  12.         .toArray(int[][]::new);
  14. System.out.println(Arrays.deepToString(res));

Output: [[2, 6], [5, 3], [5, 1]]

It streams the 2D array and for each row, it builds a 1D array by picking the columns from startColumn to endColumn inclusive and collects every array in a 2D array.

答案2

得分: 2

有个教训在其中。

从一个二维数组中挑选几行更容易。
所以也许将列"表示"为行。

  1. int[][] arr = {
  2.         {1, 2, 2},
  3.         {2, 5, 5},
  4.         {6, 3, 1},
  5.         {4, 9, 3}
  6. };
  8. int[][] sub = new int[] {
  9.         Arrays.copyOf(arr[1], 3),
  10.         Arrays.copyOf(arr[2], 3)
  11. };
  13. int[][] sharing = Arrays.copyOfRange(arr, 1, 3); // 3 是不包括的。
  15. 最后的 `sharing` 与 `arr` 共享行（列）。
  17. 一个可以创建自己的矩阵类。
  19. > 这背后有一个故事。亚洲的[_珠算_][1]与罗马的 _算盘_ 相比旋转了90°。在我看来，这使它更易读，因为它用于阅读数字，而 _珠算_ 确实是一个很好的教育工具和有用的工具。
  21. 工具：[`Arrays.copyOfRange​(T[],int,int)`][2]。
  23.   [1]: https://en.wikipedia.org/wiki/Soroban
  24.   [2]: https://docs.oracle.com/javase/10/docs/api/java/util/Arrays.html#copyOfRange(T%5B%5D,int,int)
  26. <details>
  27. <summary>英文:</summary>
  29. There is a lesson in this.
  31. It is easier to pick out a couple of rows of a two dimensional array.
  32. So maybe _represent_ columns as rows.
  34.     int[][] arr = {
  35.             {1, 2, 2},
  36.             {2, 5, 5},
  37.             {6, 3, 1},
  38.             {4, 9, 3}
  39.     };
  41.     int[][] sub = new int[] {
  42.             Arrays.copyOf(arr[1], 3),
  43.             Arrays.copyOf(arr[2], 3)
  44.     };
  46.     int[][] sharing = Arrays.copyOfRange(arr, 1, 3); // 3 exclusive.
  48. The last `sharing` shares the rows (columns) with `arr`.
  50. One could make one&#39;s matrix class.
  52. &gt; There is a story behind this. The Asian [_soroban_][1] is 90&#176; rotated with respect to the Roman _abacus_. This makes it more readable IMHO, as reading numbers, and the _soroban_ indeed is still a good pedagogical and useful tool.
  54. Utilities: [`Arrays.copyOfRange​(T[],int,int)`][2].
  57.   [1]: https://en.wikipedia.org/wiki/Soroban
  58.   [2]: https://docs.oracle.com/javase/10/docs/api/java/util/Arrays.html#copyOfRange(T%5B%5D,int,int)
  61. </details>
  65. # 答案3
  66. **得分**: 1
  68. 要从现有的二维数组中获取一个二维子数组 - 您可以遍历此数组的行，对于每一行，使用 [`Arrays.stream(int[],int,int)`][1] 方法遍历*指定的范围*：
  70. ```java
  71. int[][] arr1 = {
  72.         {1, 2, 6, 4},
  73.         {2, 5, 3, 9},
  74.         {2, 5, 1, 3}};
  1. int[][] arr2 = Arrays.stream(arr1)
  2.         // 范围从 '1'（包括）到 '3'（不包括）
  3.         .map(row -> Arrays.stream(row, 1, 3).toArray())
  4.         .toArray(int[][]::new);
  1. // 输出
  2. Arrays.stream(arr2).map(Arrays::toString).forEach(System.out::println);
  1. [2, 6]
  2. [5, 3]
  3. [5, 1]
英文:

To get a 2d sub-array from an existing 2d array - you can iterate over the rows of this array, and for each row, iterate over the specified range using the Arrays.stream(int[],int,int) method:

  1. int[][] arr1 = {
  2.         {1, 2, 6, 4},
  3.         {2, 5, 3, 9},
  4.         {2, 5, 1, 3}};
  1. int[][] arr2 = Arrays.stream(arr1)
  2.         // range from &#39;1&#39; inclusive to &#39;3&#39; exclusive
  3.         .map(row -&gt; Arrays.stream(row, 1, 3).toArray())
  4.         .toArray(int[][]::new);
  1. // output
  2. Arrays.stream(arr2).map(Arrays::toString).forEach(System.out::println);
  1. [2, 6]
  2. [5, 3]
  3. [5, 1]

huangapple
  • 本文由 发表于 2020年7月29日 02:29:33
  • 转载请务必保留本文链接：https://go.coder-hub.com/63140585.html
  • arrays
  • java
  • multidimensional-array
  • sub-array
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