求一组对象的平均值

Posted 2023-02-22

【中文标题】求一组对象的平均值

【英文标题】：find average of an array of objects

【发布时间】：2019-04-05 23:08:01

【问题描述】：

我试图找出给定数组中女性的平均值

sortArray([
    name:'Sarah', gender:'female', age:25,
    name:'Tom', gender:'male', age:18,
    name:'Tim', gender:'male', age:65,
    name:'Kim', gender:'female', age:58
]);

这就是我下面的内容

function averageFemale(list)

    let sum = 0;
    let femaleCount = 2;
    let avg = sum / femaleCount;

    for (let i = 0, i < list.length; i++)
    
        sum += list[i];
    

    return avg;

【问题讨论】：

你想平均他们的年龄吗？因为如果是这样，那么你真的应该在你的函数中的某个时刻使用他们的年龄。

你正在尝试解决这个代码战争 kata :D codewars.com/kata/5aa1931311dbd9358b000823/train/javascript

【参考方案1】：

您可以将“女性”过滤到一个新数组中，然后将其减少到所有年龄的总和，然后使用女性数组的长度除以总数：

const people = [name:'Sarah', gender:'female', age:25, name:'Tom', gender:'male', age:18, name:'Tim', gender:'male', age:65, name:'Kim', gender:'female', age:58];

const females = people.filter(person => person.gender === 'female');

const average = females.reduce((total, next) => total + next.age, 0) / females.length;

console.log(average);

【参考方案2】：

您还可以：

使用.filter() 过滤输入数组以仅获取具有gender 为female 的对象。 使用.reduce() 获取年龄总和。 通过将上述计算的总和除以过滤数组中的对象数来计算平均值。

演示：

let data = [
  name:'Sarah', gender:'female', age:25,
  name:'Tom', gender:'male', age:18,
  name:'Tim', gender:'male', age:65,
  name:'Kim', gender:'female', age:58
];

let filteredData = data.filter(( gender ) => gender == 'female'),
    avg = filteredData.reduce((r, c) => r + c.age, 0) / filteredData.length;
                 
console.log(avg);

【讨论】：

如果你想单行，那么你可以考虑在归约函数中使用 source-array 参数，并在累加之前将 c.age 除以数组长度。即：reduce((r,c,i,a)=> r+c.age/a.length,0)

【参考方案3】：

您需要在将年龄添加到sum 之前检查性别，并且还要增加femaleCount 而不是将其硬编码为2。

也不需要每次循环都重新计算avg，最后一次就可以了。

function averageFemale(list) 
  let sum = 0;
  let femaleCount = 0;
  for (let i = 0; i < list.length; i++) 
    if (list[i].gender == 'female') 
      sum += list[i].age;
      femaleCount++;
    
  
  if (femaleCount == 0) 
    return 0; // prevent division by 0
  
  let avg = sum / femaleCount;
  return avg;


console.log(averageFemale([name:'Sarah', gender:'female', age:25, name:'Tom', gender:'male', age:18, name:'Tim', gender:'male', age:65, name:'Kim', gender:'female', age:58]));

for 循环标头中还有一个错字，, 应该是 ;。

【参考方案4】：

你可以用一个 reduce 来做到这一点

function averageBy(arr) 
    const total, count = arr.reduce((a, b) => 
            if (b.gender === 'female') 
                a.total += b.age;
                a.count++;
            
            return a;
        , total: 0, count: 0);
    
    return total / count;


console.log(averageBy(arr));

<script>
const arr = [
    
        name: 'Sarah',
        gender: 'female',
        age: 25
    ,
    
        name: 'Tom',
        gender: 'male',
        age: 18
    ,
    
        name: 'Tim',
        gender: 'male',
        age: 65
    ,
    
        name: 'Kim',
        gender: 'female',
        age: 58
    
];
</script>

【参考方案5】：

const arr= [
    name:'Sarah', gender:'female', age:25,
    name:'Tom', gender:'male', age:18,
    name:'Tim', gender:'male', age:65,
    name:'Kim', gender:'female', age:58
]


function averageAgeByGender(array,gender)
  const getGender = (elem) => elem.gender===gender
  const average = (a,b, i, self)=> (a+b.age/self.length)
  return array.filter(getGender).reduce(average,0)


console.log(averageAgeByGender(arr,'female'))

【参考方案6】：

您需要检查gender 属性并取和age 并增加一个计数器，因为您事先并不知道。

function averageFemale(list) 
    var sum = 0,
        count = 0,
        i;

    for (i = 0; i < list.length; i++) 
        if (list[i].gender === 'female') 
            sum += list[i].age;
            ++count;
        
    
    return sum / count;


var array = [ name: 'Sarah', gender: 'female', age: 25 ,  name: 'Tom', gender: 'male', age: 18 ,  name: 'Tim', gender: 'male', age: 65 ,  name: 'Kim', gender: 'female', age: 58 ];

console.log(averageFemale(array));

【参考方案7】：

这是一种通过减少女性年龄并除以女性总数的方法：

const data = [name:'Sarah', gender:'female', age:25, name:'Tom', gender:'male', age:18, name:'Tim', gender:'male', age:65, name:'Kim', gender:'female', age:58];

let count = 0;
const average = data.reduce((total, person) => 
  if (person.gender === 'female') 
  	total += person.age;
    count++;
  
  return total;
, 0) / count;

console.log(average);

【参考方案8】：

这只是我的方法（只在数组上循环一次），并且基于下一个用于逐步计算平均值的数学公式：

avgN = (x1 + ... + xN) / N = (x1 + ... + xN-1) / N + (xN / N)

     = (x1 + ... + xN-1) * (N-1) / (N * (N-1)) + (xN / N)

     = ((x1 + ... + xN-1) / (N-1)) * ((N-1) / N) + (xN / N)

     = avgN-1 * (N-1) / N + (xN / N)

     = ((N-1) avgN-1 + xN) / N

var sortArray = [
    name:'Sarah', gender:'female', age:25,
    name:'Tom', gender:'male', age:18,
    name:'Tim', gender:'male', age:65,
    name:'Kim', gender:'female', age:58
];

function averageFemale(list)

    var count = 0;

    return list.reduce((avg, personData) =>
    
        if (personData.gender === 'female')
            avg = (count * avg + personData.age) / (++count);

        return avg;
    ,0);


console.log("Average age of females is: " + averageFemale(sortArray));

【参考方案9】：

这是我的解决方案，我觉得它更灵活：

function sumOfArrayWithParameter (array, parameter) 
  let sum = null;
  if (array && array.length > 0 && typeof parameter === 'string') 
    sum = 0;
    for (let e of array) if (e && e.hasOwnProperty(parameter)) sum += e[parameter];
  
  return sum;

要获得平均值，您只需像这样使用它：

let sum = sumOfArrayWithParameter(array, 'age');
let avg = sum / array.length;