如何解决按每行的平均值对二维数组进行排序
我有复杂的任务来手动对二维数组进行不同的排序。 到目前为止，我完成了这些任务：
-
用户需要输入 10 - 20 的行大小，
-
生成二维数组，其中行大小是用户输入，列大小是从 10-50 随机生成的，
-
每个数组都填充了 100 - 999 之间随机生成的数字，
-
按降序输出每个数组行，
-
输出每个数组行的平均值，
-
以最大平均值输出到屏幕阵列上，
-
到目前为止我无法解决任务编号。 7. 输出按每行平均值排序的二维数组。 试图在循环中实现新的 arrayAverage 来对它不起作用的行进行排序。 数组只需要排序，无需创建新数组。
import java.util.Arrays;
import java.util.Random;
import java.util.Scanner;
public class SortArray2D {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Sorting two dimennsional arrays!!!");
System.out.print("Enter arrays 1st dimmension size 10 - 20: ");
int array1stDsize = sc.nextInt();
int array2ndDsize = new Random().nextInt(40) + 10;
System.out.println();
sc.close();
if (array1stDsize > 20 || array1stDsize < 10) {
System.out.println("The number you enteraed is too big or too small!!!");
} else {
//initializing array
int[][] array = new int[array1stDsize][array2ndDsize];
for (int i = 0; i < array.length; i = i + 1) {
for (int j = 0; j < array[i].length; j = j + 1) {
int input = new Random().nextInt(900) + 100;
array[i][j] = input;
}
}
System.out.println("Array element output: ");
arrayOutput(array);
// array element sorting from biggest to smallest
for (int k = 0; k < array.length; k++) {
for (int i = 1; i < array[k].length; i++) {
for (int j = i; j > 0; j--) {
if (array[k][j] > array[k][j - 1]) {
int element = array[k][j];
array[k][j] = array[k][j - 1];
array[k][j - 1] = element;
}
}
}
}
System.out.println();
System.out.println("Descending Array element output: ");
arrayOutput(array);
System.out.println();
System.out.println("Average value output by array: ");
float[] arrayAverage = new float[array1stDsize];
float average = 0;
for (int i = 0; i < array.length; i = i + 1) {
for (int j = 0; j < array[i].length; j = j + 1) {
average = average + array[i][j];
}
average = (float) (Math.round((average / array[i].length) * 100.0) / 100.0);
System.out.println(i + ". array average value: " + average);
arrayAverage[i] = average;
}
System.out.println();
System.out.println("New array from average values: ");
System.out.println(Arrays.toString(arrayAverage));
System.out.println();
System.out.println("Most valuest array is: ");
double max = 100;
int row = 0;
for (int i = 0; i < arrayAverage.length; i++) {
if (max < arrayAverage[i]) {
max = arrayAverage[i];
row = i;
}
}
System.out.print("Its founded " + row + ". row and it's value is: ");
for (int j = 0; j < array[row].length; j = j + 1) {
System.out.print(" " + array[row][j]);
}
System.out.println();
System.out.println();
//2D array sorting by average values
}
}
public static int[][] arrayOutput(int[][] array) {
for (int i = 0; i < array.length; i = i + 1) {
for (int j = 0; j < array[i].length; j = j + 1) {
if (j == 0) {
System.out.print("{ " + array[i][j]);
} else {
System.out.print("," + array[i][j]);
}
}
System.out.print(" }");
System.out.println();
}
return array;
}
}
解决方法
计算平均值的代码部分：
float[] arrayAverage = new float[array1stDsize];
float average = 0;
for (int i = 0; i < array.length; i = i + 1) {
for (int j = 0; j < array[i].length; j = j + 1) {
average = average + array[i][j];
}
average = (float) (Math.round((average / array[i].length) * 100.0) / 100.0);
System.out.println(i + ". array average value: " + average);
arrayAverage[i] = average;
}
有点错误，您需要在计算下一行的平均值之前将 average 变量设置为零：
...
arrayAverage[i] = average;
average = 0;
使用 Java Streams 可以非常优雅地按行的平均值对矩阵进行排序，即：
Arrays.sort(array,comparingDouble(row -> IntStream.of(row)
.average()
.getAsDouble()));
使用Arrays.sort方法对数组进行排序，然后对每一行取其平均值作为双精度值IntStream.of(row).average().getAsDouble()，并用作排序参数comparingDouble(....)。>
运行示例：
import java.util.Arrays;
import java.util.Comparator;
import java.util.stream.IntStream;
import static java.util.Comparator.comparingDouble;
public class Test {
public static void main(String[] args) {
int array[][] = {{10,20,30},{40,50,60},{1,2,3} };
Arrays.sort(array,comparingDouble(row -> IntStream.of(row).average().getAsDouble()));
Arrays.stream(array).map(Arrays::toString).forEach(System.out::println);
}
}
输出：
[1,3]
[10,30]
[40,60]
对于相反的顺序，请改用：
Arrays.sort(array,comparing(row -> IntStream.of(row).average().getAsDouble(),reverseOrder()));
输出：
[40,60]
[10,30]
[1,3]
编辑：没有流
不使用流，您可以执行以下操作：
1 - 获取矩阵行平均值的数组：
float[] arrayAverage = average(matrix);
您已经知道如何计算平均值，因此您只需要从您创建的代码中提取一个方法，即：
private static float[]average(int[][] array) {
float[] arrayAverage = new float[array.length];
float sum = 0;
for (int i = 0; i < array.length; i++) {
for (int j = 0; j < array[i].length; j++) {
sum += array[i][j];
}
arrayAverage[i] = (float) (Math.round((sum / array[i].length) * 100.0) / 100.0);
sum = 0;
}
return arrayAverage;
}
2 - 创建一个数组来表示行并初始化如下：
int [] row_position = new int [arrayAverage.length];
for(int i = 0; i < row_position.length; i++)
row_position[i] = i;
3 - 使用最简单的排序（冒泡排序）对 arrayAverage 进行排序。在对该数组进行排序时，相应地更新存储在 row_position 上的位置：
for(int i=0; i < arrayAverage.length; i++){
for(int j=1; j < (arrayAverage.length-i); j++){
if(arrayAverage[j-1] > arrayAverage[j]){
float temp = arrayAverage[j-1];
arrayAverage[j-1] = arrayAverage[j];
arrayAverage[j] = temp;
int temp_pos = row_position[j-1];
row_position[j-1] = row_position[j];
row_position[j] = temp_pos;
}
}
}
4 - 现在您有了 row_positions 数组，它告诉您应该如何重新排列已排序的行，您只需要相应地交换行：
int[][] tmp_matrix = new int [matrix.lenght][];
for (int i = 0; i < tmp_matrix.length; i++) {
tmp_matrix[i] = matrix[row_position[i]];
}
matrix = new_matrix;
但是请记住，为了简单起见，我假设了一个 NxN 的二次矩阵，并且可以在性能方面改进上述解决方案。
最后，让它工作，看起来像这样。
import java.util.Arrays;
import java.util.Random;
import java.util.Scanner;
public class SortArray2D {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Sorting two dimennsional arrays!!!");
System.out.print("Enter arrays 1st dimmension size 10 - 20: ");
int array1stDsize = sc.nextInt();
System.out.println();
sc.close();
if (array1stDsize > 20 || array1stDsize < 10) {
System.out.println("The number you enteraed is too big or too small!!!");
} else {
int[][] array = new int[array1stDsize][];
Random random = new Random();
for (int i = 0; i < array.length; i++) {
array[i] = new int[random.nextInt(31) + 10];
for (int j = 0; j < array[i].length; j++) {
int input = new Random().nextInt(900) + 100;
array[i][j] = input;
}
}
System.out.println("Array element output: ");
arrayOutput(array);
// array element sorting from biggest to smallest
for (int k = 0; k < array.length; k++) {
for (int i = 1; i < array[k].length; i++) {
for (int j = i; j > 0; j--) {
if (array[k][j] > array[k][j - 1]) {
int element = array[k][j];
array[k][j] = array[k][j - 1];
array[k][j - 1] = element;
}
}
}
}
System.out.println();
System.out.println("Descending Array element output: ");
arrayOutput(array);
System.out.println();
System.out.println("Average value output by array: ");
float[] arrayAverage = new float[array1stDsize];
for (int i = 0; i < array.length; i = i + 1) {
float sum = 0;
for (int j = 0; j < array[i].length; j = j + 1) {
sum = sum + array[i][j];
}
float average = (float) (Math.round((sum / array[i].length) * 100.0) / 100.0);
System.out.println(i + ". array average value: " + average);
arrayAverage[i] = average;
}
// array lines sorting from by average value increasing
for (int i = 0; i < arrayAverage.length; i = i + 1) {
for (int j = i; j > 0; j--) {
if (arrayAverage[j] < arrayAverage[j - 1]) {
float tmpor = arrayAverage[j];
arrayAverage[j] = arrayAverage[j - 1];
arrayAverage[j - 1] = tmpor;
int[] tmp = array[j];
array[j] = array[j - 1];
array[j - 1] = tmp;
}
}
}
System.out.println();
System.out.print("Array from average values sorted: ");
System.out.println(Arrays.toString(arrayAverage));
System.out.println();
System.out.println("Incerasing Array line output: ");
arrayOutput(array);
System.out.println();
System.out.print("Most valuest array is array: ");
double max = 100;
int row = 0;
for (int i = 0; i < arrayAverage.length; i++) {
if (max < arrayAverage[i]) {
max = arrayAverage[i];
row = i;
}
}
for (int j = 0; j < array[row].length; j = j + 1) {
System.out.print(" " + array[row][j]);
}
}
}
public static int[][] arrayOutput(int[][] array) {
for (int i = 0; i < array.length; i = i + 1) {
for (int j = 0; j < array[i].length; j = j + 1) {
if (j == 0) {
System.out.print("{ " + array[i][j]);
} else {
System.out.print("," + array[i][j]);
}
}
System.out.print(" }");
System.out.println();
}
return array;
}
}
输出按升序排序的二维数组：
int[][] arr = {
{12,54,87},// avg 51
{98,56,32},// avg 62
{19,73,46}}; // avg 46
Arrays.stream(arr)
// sort an array by the
// average value of the row
.sorted(Comparator.comparingDouble(row ->
// get the average value or 0 if the row is empty {}
Arrays.stream(row).average().orElse(0)))
// string representation
// of the row content
.map(Arrays::toString)
// output line by line
.forEach(System.out::println);
输出：
[19,46]
[12,87]
[98,32]
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