平均二维数组列

Question

我正在尝试计算二维数组列的平均值。我的代码似乎将行中的数字相加，然后除以总数。在这个例子中应该只有 4 次赋值，但它循环了 12 次。有人知道我的代码有什么问题吗？这些数字是从一个文本文件输入的，在完整代码中更高（不确定是否会影响它）。

示例数组：

[2,3,6,7]
[4,5,6,7]
[2,2,2,2]

System.out.println("Average score of each assignment:");
//TODO: compute and print the average on each assignment
double total = 0;
int totallength = 0;
int assignment = 1;
for (int i = 0; i < myArray.length; i++) {
    for (int j = 0; j < myArray[i].length; j++) {
        total += myArray[i][j];
        totallength++;
        System.out.println("Assignment #" + assignment++
                + " Average: " + (total / totallength));
    }
}

这是我的输出：

Average score of each assignment:
Assignment #1 Average: 2.0
Assignment #2 Average: 2.5
Assignment #3 Average: 3.6666666666666665
Assignment #4 Average: 4.5
Assignment #5 Average: 4.4
Assignment #6 Average: 4.5
Assignment #7 Average: 4.714285714285714
Assignment #8 Average: 5.0
Assignment #9 Average: 4.666666666666667
Assignment #10 Average: 4.4
Assignment #11 Average: 4.181818181818182
Assignment #12 Average: 4.0

期望的输出：

Assignment #1 Average: 2.666666666
Assignment #2 Average: 3.333333333
Assignment #3 Average: 4.666666666
Assignment #4 Average: 5.333333333

Answer 1

如果你想得到每一行的平均值，你需要在每个其他循环上初始化你的总计数器，并且在求和后只在外循环上打印：

int assignment=1;
for(int i=0;i<myArray.length;i++) {
    // initialize here, to start each row separatly
    double total=0;
    int totallength=0;
    for(int j=0;j<myArray[i].length;j++) {
        total+=myArray[i][j];
        totallength++;
    }
    // print after the loop, so it will be done only once per row
    System.out.println("Assignment #" + assignment++ + " Average: " + (total/totallength));
}

顺便说一句，计算平均值的更简单方法是利用 java 8 流功能：

for(int i=0;i<myArray.length;i++) {
  double average = Arrays.stream(myArray[i]).average().orElse(0d);
}

Answer 2

您可以按照以下方式进行：

public class Main {
    public static void main(String[] args){
        int [][]myArray= {
                {2,3,6,7},
                {4,5,6,7},
                {2,2,2,2},
        };      
        double total=0;
        int assignment=1;

        System.out.println("Average score of each assignment:");
        for(int i=0;i<myArray[0].length;i++) {
            for(int j=0;j<myArray.length;j++) {
                total+=myArray[j][i];          
            }
            System.out.println("Assignment #" + assignment++ + " Average: " + (total/3));
            total=0;
        }
    }
}

输出：

Average score of each assignment:
Assignment #1 Average: 2.6666666666666665
Assignment #2 Average: 3.3333333333333335
Assignment #3 Average: 4.666666666666667
Assignment #4 Average: 5.333333333333333

Answer 3

您可以使用IntStream.average()方法：

int m = 3;
int n = 4;
int[][] arr = {
        {2, 3, 6, 7},
        {4, 5, 6, 7},
        {2, 2, 2, 2}};

double[] averages = IntStream.range(0, n)
        .mapToDouble(i -> IntStream.range(0, m)
                .map(j -> arr[j][i])
                .average()
                .orElse(0))
        .toArray();

// output
IntStream.range(0, averages.length).forEach(i ->
        System.out.println("Assignment #" + (i + 1)
                + " Average: " + (averages[i])));

Assignment #1 Average: 2.6666666666666665
Assignment #2 Average: 3.3333333333333335
Assignment #3 Average: 4.666666666666667
Assignment #4 Average: 5.333333333333333

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