更新分级评价

whycxzp

2022-10-10 af0697a5241328994ff0badeb53e095f1eb63183

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
package com.whyc.util;
 
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
 
public class MathUtil {
 
    public static float getStandardDeviation(List<Float> list){
        //求平均值
        float avg = list.stream().collect(Collectors.averagingDouble(Float::floatValue)).floatValue();
 
        //求方差
        //相减,平方,累加
        float subSquareTotal = 0.0f;
        for (Float item : list) {
            subSquareTotal += (item -avg)*(item -avg);
        }
        Float s = subSquareTotal/list.size();
        //标准差
        double σ = Math.sqrt(s.doubleValue());
        return BigDecimal.valueOf(σ).setScale(4, RoundingMode.HALF_UP).floatValue();
    }
 
    public static void main(String[] args) {
        Float[] f = {3.54f,3.55f,3.55f,3.56f,3.57f,3.56f,3.58f,3.58f,3.56f};
        Float[] f2 = {3.53f,3.55f,3.56f,3.57f,3.59f,3.58f,3.6f,3.6f,3.61f};
        Float standardDeviation = getStandardDeviation(Arrays.asList(f));
        Float standardDeviation2 = getStandardDeviation(Arrays.asList(f2));
        System.out.println(standardDeviation);
        System.out.println(standardDeviation2);
    }
}