Java: Sort an Array Based on the Index Order of Another Array

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英文:

Java: Sort an Array Based on the Index Order of Another Array

问题

In Java, you can sort one array based on the index order of another sorted array by creating a custom comparator and using it with a sorting algorithm like Arrays.sort(). Here's an example of how you can do it:

import java.util.Arrays;
import java.util.Comparator;

public class Main {
    public static void main(String[] args) {
        int[] arr1 = {26, 8, 3};
        int[] arr2 = {3, 1, 2};
        int[] arr3 = {57, 23, 11};
        int[] arr4 = {78, 2, 61};

        // Sort arr2 in ascending order
        Arrays.sort(arr2);

        // Create an index array to track the original positions
        Integer[] indexes = new Integer[arr2.length];
        for (int i = 0; i < indexes.length; i++) {
            indexes[i] = i;
        }

        // Sort arr1, arr3, and arr4 based on the sorted order of arr2
        Arrays.sort(indexes, Comparator.comparingInt(i -> arr2[i]));

        int[] newArr1 = new int[arr1.length];
        int[] newArr3 = new int[arr3.length];
        int[] newArr4 = new int[arr4.length];

        for (int i = 0; i < arr2.length; i++) {
            newArr1[i] = arr1[indexes[i]];
            newArr3[i] = arr3[indexes[i]];
            newArr4[i] = arr4[indexes[i]];
        }

        // newArr1, newArr3, and newArr4 now contain the sorted values
        System.out.println("arr1 = " + Arrays.toString(newArr1));
        System.out.println("arr3 = " + Arrays.toString(newArr3));
        System.out.println("arr4 = " + Arrays.toString(newArr4));
    }
}

This code first sorts arr2, then creates an index array to track the original positions. After that, it sorts arr1, arr3, and arr4 based on the sorted order of arr2 using the index array.

英文:

In Java, how can I sort an array based on the index order of another sorted array? For instance, if I have:

arr1 = {26, 8, 3}
arr2 = {3, 1, 2}
arr3 = {57, 23, 11}
arr4 = {78, 2, 61}

and I sort arr2 in ascending order to be

arr2 = {1, 2, 3}

and I want the other to then be:

arr1 = {8, 3, 26}
arr3 = {23, 11, 57}
arr4 = {2, 61, 78}

How can I accomplish this is Java? I know I would save the new sorted arrays into new instances. Anything helps, thanks!

答案1

得分: 0

这是一种方法来完成它。

  • 根据数组的内容对目标数组的索引进行排序。
  • 然后使用该索引数组将所有数组映射到基于索引的数组上。
Integer[] indices = IntStream.range(0, arr2.length)
        .boxed()
        .sorted(Comparator.comparing(i -> arr2[i]))
        .toArray(Integer[]::new);

List<int[]> list = Stream
        .of(arr1, arr2, arr3, arr4).map(arr -> Stream
                .of(indices)
                .mapToInt(i -> arr[i])
                .toArray())
        .collect(Collectors.toList());

list.forEach(arr -> System.out.println(Arrays.toString(arr)));

打印结果如下:

[8, 3, 26]
[1, 2, 3]
[23, 11, 57]
[2, 61, 78]

您还可以将这些数组放入另一个“2D”数组中,然后按照相同的方式进行操作,结果相同。

int[][] arrays = { arr1, arr2, arr3, arr4 };

List<int[]> list = Arrays
        .stream(arrays)
        .map(arr -> Stream
                .of(indices)
                .mapToInt(i -> arr[i])
                .toArray())
        .collect(Collectors.toList());

注意:上述代码示例中的字符转义是HTML实体编码,您可能需要将其还原为标准的字符。

英文:

Here is one way to do it.

  • sort the indices of the target array based on the arrays contents.
  • then use that index array to map all the arrays based on the indexed one.
Integer[] indices = IntStream.range(0, arr2.length)
.boxed()                 
.sorted(Comparator.comparing(i -&gt; arr2[i]))        
.toArray(Integer[]::new);
List&lt;int[]&gt; list = Stream
.of(arr1, arr2, arr3, arr4).map(arr -&gt; Stream
.of(indices)
.mapToInt(i -&gt; arr[i])
.toArray())
.collect(Collectors.toList());
list.forEach(arr -&gt; System.out.println(Arrays.toString(arr))); 

Prints

[8, 3, 26]
[1, 2, 3]
[23, 11, 57]
[2, 61, 78]

You could also place the arrays in another &quot;2D&quot; array and do as follow with the same result.

int[][] arrays = { arr1, arr2, arr3, arr4 };
List&lt;int[]&gt; list = Arrays
.stream(arrays)
.map(arr -&gt; Stream
.of(indices)
.mapToInt(i -&gt; arr[i])
.toArray())
.collect(Collectors.toList());
</details>
# 答案2
**得分**: 0
以下是代码的翻译部分:
```java
public class SortTogether {
// 对数组 a 进行排序,并根据 a 的索引更新数组 b、c 和 d 中的元素
public static void bubbleSort(int[] a, int[] b, int[] c, int[] d) {
for (int i = 0; i < a.length; i++) {
for (int j = 0; j < a.length - i - 1; j++) {
if (a[j] > a[j + 1]) {
// 在交换元素时
int t = a[j];
a[j] = a[j + 1];
a[j + 1] = t;
// 同时交换其他数组中的元素
// 以确保其他数组中的元素也保持在一起
t = b[j];
b[j] = b[j + 1];
b[j + 1] = t;
t = c[j];
c[j] = c[j + 1];
c[j + 1] = t;
t = d[j];
d[j] = d[j + 1];
d[j + 1] = t;
}
}
}
}
public static void main(String a[]) {
int[] arr1 = {26, 8, 3};
int[] arr2 = {3, 1, 2};
int[] arr3 = {57, 23, 11};
int[] arr4 = {78, 2, 61};
System.out.println("排序前");
display(arr1);
display(arr2);
display(arr3);
display(arr4);
bubbleSort(arr2, arr1, arr3, arr4);
System.out.println("\n排序后");
display(arr1);
display(arr2);
display(arr3);
display(arr4);
}
public static void display(int[] arr) {
for (int num : arr) System.out.printf("%4d", num);
System.out.println();
}
}

请注意,我已经将 HTML 实体 &lt;&quot; 替换为了正常的符号。

英文:

Found answer elsewhere

public class SortTogether{
// sort the array a, and also update the elements in array b, c, and d
// based on the index of a
public static void bubbleSort(int[] a, int[] b, int[] c, int[] d) {
for(int i=0; i&lt;a.length; i++){
for(int j=0; j&lt;a.length-i-1;j++){
if(a[j]&gt;a[j+1]){
// when you are swapping the elements
int t = a[j]; a[j]=a[j+1];a[j+1]=t;
// swap the elements in the other arrays as well
// so the elements in other array will also stay together
t = b[j]; b[j]=b[j+1];b[j+1]=t;
t = c[j]; c[j]=c[j+1];c[j+1]=t;
t = d[j]; d[j]=d[j+1];d[j+1]=t;
}
}
}
}
public static void main(String a[]) {
int[] arr1 = {26, 8, 3};
int[] arr2 = {3, 1, 2};
int[] arr3 = {57, 23, 11};
int[] arr4 = {78, 2, 61};
System.out.println(&quot;Before sort&quot;);
display(arr1);
display(arr2);
display(arr3);
display(arr4);
bubbleSort(arr2,arr1,arr3,arr4);
System.out.println(&quot;\nAfter sort&quot;);
display(arr1);
display(arr2);
display(arr3);
display(arr4);
}
public static void display(int[] arr) {
for (int num : arr) System.out.printf(&quot;%4d&quot;, num);
System.out.println();
}
}

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  • 本文由 发表于 2020年7月28日 03:24:26
  • 转载请务必保留本文链接:https://go.coder-hub.com/63122160.html
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