java 你如何在java中正确附加两个二维数组？
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How do you append two 2D array in java properly?
提问by Cferrel
I have been trying to append two 2 D arrays in java. Is it possible to get an example because I have been trying to look it up but cannot find one.
我一直在尝试在 java 中附加两个二维数组。是否有可能得到一个例子，因为我一直试图查找它但找不到一个。
int [][]appendArray(empty,window)
{
int [][]result= new int [empty.length][empty[0].length+window[0].length];
}
回答by MeBigFatGuy
Here you go:
干得好：
import java.util.Arrays;
public class Array2DAppend {
public static void main(String[] args) {
int[][] a = new int[][] {{1, 2}, {3, 4}};
int[][] b = new int[][] {{1, 2, 3}, {3, 4, 5}};
System.out.println(Arrays.deepToString(a));
System.out.println(Arrays.deepToString(b));
System.out.println(Arrays.deepToString(append(a, b)));
}
public static int[][] append(int[][] a, int[][] b) {
int[][] result = new int[a.length + b.length][];
System.arraycopy(a, 0, result, 0, a.length);
System.arraycopy(b, 0, result, a.length, b.length);
return result;
}
}
and the output:
和输出：
[[1, 2], [3, 4]]
[[1, 2, 3], [3, 4, 5]]
[[1, 2], [3, 4], [1, 2, 3], [3, 4, 5]]
回答by Tobber
If I understand you correctly, you want to append it, in the opposite dimension, than DomS and MeBigFatGuy thinks. If I'm is correct there are two ways:
如果我理解正确，您想将它附加到与 DomS 和 MeBigFatGuy 认为相反的维度上。如果我是对的，有两种方法：
If the "column" height (length of 2nd dimension) are fixed within each array you can use this method. It leaves blank (zero-filled) cells, if the arrays have different length of the first dimension. Tho make this code safer, you might want to
如果每个数组中的“列”高度（第二维的长度）是固定的，则可以使用此方法。如果数组的第一维长度不同，它会留下空白（零填充）单元格。使此代码更安全，您可能想要
/**
* For fixed "column" height. "Blank cells" will be left, if the two arrays have different "width"
*/
static int[][] appendArray2dFix(int[][] array1, int[][] array2){
int a = array1[0].length, b = array2[0].length;
int[][] result = new int[Math.max(array1.length,array2.length)][a+b];
//append the rows, where both arrays have information
int i;
for (i = 0; i < array1.length && i < array2.length; i++) {
if(array1[i].length != a || array2[i].length != b){
throw new IllegalArgumentException("Column height doesn't match at index: " + i);
}
System.arraycopy(array1[i], 0, result[i], 0, a);
System.arraycopy(array2[i], 0, result[i], a, b);
}
//Fill out the rest
//only one of the following loops will actually run.
for (; i < array1.length; i++) {
if(array1[i].length != a){
throw new IllegalArgumentException("Column height doesn't match at index: " + i);
}
System.arraycopy(array1[i], 0, result[i], 0, a);
}
for (; i < array2.length; i++) {
if(array2[i].length != b){
throw new IllegalArgumentException("Column height doesn't match at index: " + i);
}
System.arraycopy(array2[i], 0, result[i], a, b);
}
return result;
}
If you want to allow the column with to vary within each array, this is possible, with a minor change. This doesn't leave any empty cells.
如果您希望允许列在每个数组内变化，这是可能的，只需稍作更改。这不会留下任何空单元格。
/**
* For variable "column" height. No "blank cells"
*/
static int[][] appendArray2dVar(int[][] array1, int[][] array2){
int[][] result = new int[Math.max(array1.length,array2.length)][];
//append the rows, where both arrays have information
int i;
for (i = 0; i < array1.length && i < array2.length; i++) {
result[i] = new int[array1[i].length+array2[i].length];
System.arraycopy(array1[i], 0, result[i], 0, array1[i].length);
System.arraycopy(array2[i], 0, result[i], array1[i].length, array2[i].length);
}
//Fill out the rest
//only one of the following loops will actually run.
for (; i < array1.length; i++) {
result[i] = new int[array1[i].length];
System.arraycopy(array1[i], 0, result[i], 0, array1[i].length);
}
for (; i < array2.length; i++) {
result[i] = new int[array2[i].length];
System.arraycopy(array2[i], 0, result[i], 0, array2[i].length);
}
return result;
}
Test code modified from DomS
从 DomS 修改的测试代码
public static void main(String[] args) {
//Test Var
int[][] array1 = new int[][] {
{1, 2, 3},
{3, 4, 5, 6},
};
int[][] array2 = new int[][] {
{11, 12, 13,14 },
{13, 14, 15, 16, 17},
};
int[][] expected = new int[][] {
{1, 2, 3, 11, 12, 13, 14},
{3, 4, 5, 6, 13, 14, 15, 16, 17}
};
int[][] appended = appendArray2dVar(array1, array2);
System.out.println("This");
for (int i = 0; i < appended.length; i++) {
for (int j = 0; j < appended[i].length; j++) {
System.out.print(appended[i][j]+", ");
}
System.out.println();
}
System.out.println("Should be the same as this");
for (int i = 0; i < expected.length; i++) {
for (int j = 0; j < expected[i].length; j++) {
System.out.print(expected[i][j]+", ");
}
System.out.println();
}
//Test Fix
array1 = new int[][] {
{1, 2, 3, 4},
{3, 4, 5, 6},
};
array2 = new int[][] {
{11, 12, 13},
{13, 14, 15},
};
expected = new int[][] {
{1, 2, 3, 4,11, 12, 13},
{3, 4, 5, 6, 13, 14, 15}
};
appended = appendArray2dFix(array1, array2);
System.out.println("This");
for (int i = 0; i < appended.length; i++) {
for (int j = 0; j < appended[i].length; j++) {
System.out.print(appended[i][j]+", ");
}
System.out.println();
}
System.out.println("Should be the same as this");
for (int i = 0; i < expected.length; i++) {
for (int j = 0; j < expected[i].length; j++) {
System.out.print(expected[i][j]+", ");
}
System.out.println();
}
}
回答by spot35
If I've understood your problem correctly, this method will append two 2d arrays together -
如果我正确理解了您的问题，此方法会将两个二维数组附加在一起 -
private static int[][] appendArrays(int[][] array1, int[][] array2) {
int[][] ret = new int[array1.length + array2.length][];
int i = 0;
for (;i<array1.length;i++) {
ret[i] = array1[i];
}
for (int j = 0;j<array2.length;j++) {
ret[i++] = array2[j];
}
return ret;
}
This quick bit of code will test it -
这段简短的代码将对其进行测试 -
int[][] array1 = new int[][] {
{1, 2, 3},
{3, 4, 5, 6},
};
int[][] array2 = new int[][] {
{11, 12, 13},
{13, 14, 15, 16},
};
int[][] expected = new int[][] {
{1, 2, 3},
{3, 4, 5, 6},
{11, 12, 13},
{13, 14, 15, 16},
};
int[][] appended = appendArrays(array1, array2);
System.out.println("This");
for (int i = 0; i < appended.length; i++) {
for (int j = 0; j < appended[i].length; j++) {
System.out.print(appended[i][j]+", ");
}
System.out.println();
}
System.out.println("Should be the same as this");
for (int i = 0; i < expected.length; i++) {
for (int j = 0; j < expected[i].length; j++) {
System.out.print(expected[i][j]+", ");
}
System.out.println();
}
回答by Liv
I'm guessing by "appending" you mean to extend the number of rows of a matrix with the rows of another? In which case the 2 array / matrices have to have the same number of columns! So for instance you can append a[7][6] with b[100][6] which will result in array c[107][6] by simply appending b's 100 rows to a's 7 rows -- but that's only because they both have 6 columns. It doesn't make sense for instance to append a[7][3] with b[100][6] ! So your function has to enforce these upfront. And no, there is no way of doing this in Java without writing your own which will be something like this:
我猜通过“附加”你的意思是用另一个矩阵的行扩展矩阵的行数？在这种情况下，2 个数组/矩阵必须具有相同的列数！因此，例如，您可以将 a[7][6] 与 b[100][6] 附加到数组 c[107][6] 中，只需将 b 的 100 行附加到 a 的 7 行——但这只是因为它们两者都有 6 列。例如将 a[7][3] 附加到 b[100][6] 是没有意义的！所以你的函数必须预先强制执行这些。不，如果不编写自己的代码，就无法在 Java 中执行此操作，如下所示：
int[][] appendArray( empty, window ) {
if( empty[0].length != window[0].length ) throw new IllegalArgumentException( "Wrong column size" );
int[][] result = new int[empty.length + window.length];
for( int i = 0; i < empty.length; i++ )
System.arrayCopy( empty[i], 0, result[0], 0, empty[i].length );
for( int i = 0; i < window.length; i++ )
System.arrayCopy( window[i], 0, result[i + empty.length], 0, window[i].length );
return result;
}
