如何在 JavaScript 中计算对象数组中给定属性的平均值

Question

我有一个对象数组。每个对象都包含一些属性，其中一个属性是年龄。

var people = [
  {
    name: 'Anna',
    age: 22
  },
  {
    name: 'Tom',
    age: 34
  }, {
    name: 'John',
    age: 12
  },
]

我想计算这个数组中所有年龄属性的平均值。我使用这个功能：

let getAverage = arr => {
  let reducer = (total, currentValue) => total + currentValue;
  let sum = arr.reduce(reducer)
  return sum / arr.length;
}

它适用于像 [22, 34, 12] 这样的简单数组，但不适用于对象数组。

如何修改我的 getAverage 函数以使其也适用于对象数组？

这是我的代码的 sn-p： https://jsfiddle.net/marektchas/kc8Ls0f5/2/

Answer 1

您无需修改​​ getAverage - 您可以在传递数组之前对其进行预处理，在这种情况下，getAverage 将完全按照需要工作：

var people = [
  {
    name: 'Anna',
    age: 22
  },
  {
    name: 'Tom',
    age: 34
  }, {
    name: 'John',
    age: 12
  },
]

let getAverage = arr => {
  let reducer = (total, currentValue) => total + currentValue;
  let sum = arr.reduce(reducer)
  return sum / arr.length;
}

let ages = people.map(person => person.age);

console.log(getAverage(ages));

如果您想更改getAverage，以便它可以处理任何潜在类型的输入，那么您可以添加一个可选参数来执行值提取，这样您就不必在每个数组上运行map .

var numbers = [
  1,
  2,
  3,
  4,
  5
]

var people = [
  {
    name: 'Anna',
    age: 22
  },
  {
    name: 'Tom',
    age: 34
  }, {
    name: 'John',
    age: 12
  },
]

var moreComplexObjects = [
  { 
    a: {
      b: {
        c: 6
      }
    }
  },
  { 
    a: {
      b: {
        c: 7
      }
    }
  },
  { 
    a: {
      b: {
        c: 8
      }
    }
  }
]

//the default value of the second parameter is a function that returns the input
let getAverage = (arr, valueExtractor = x => x) => { 

  //extract the value of each element
  let reducer = (total, currentValue) => total + valueExtractor(currentValue);
  let sum = arr.reduce(reducer, 0) //make sure you add an initialiser
  return sum / arr.length;
}

const ageExtractor = person => person.age;
const complexKeyExtractor = obj => obj.a.b.c;

console.log(getAverage(numbers));
console.log(getAverage(people, ageExtractor));
console.log(getAverage(moreComplexObjects, complexKeyExtractor));

上面的注释，如果您不向Array#reduce 提供第二个参数，那么它运行total 的第一次 时间将是数组的第一个元素，但是second 次及以后，将是迄今为止的总和。这种情况不值得处理，所以提供一个初始值就可以解决。

Answer 2

您可以使用reduce() 并将数组中每个对象的属性age 添加到ac。不要忘记传递0（ac 的初始值）作为第二个参数，否则它会返回NaN

var people = [
  {
    name: 'Anna',
    age: 22
  },
  {
    name: 'Tom',
    age: 34
  }, {
    name: 'John',
    age: 12
  },
]

let avgs = people.reduce((ac,a) => a.age + ac,0)/people.length
console.log(avgs)

Answer 3

您可以为想要的属性提供一个函数并使用起始值进行缩减。

const
    getAverage = (array, fn = v => v) => {
        var reducer = fn => (total, item) => total + fn(item),
            sum = array.reduce(reducer(fn), 0);
        return sum / array.length;
    };

var people = [{ name: 'Anna', age: 22 }, { name: 'Tom', age: 34 }, { name: 'John', age: 12 }];

console.log(getAverage(people, o => o.age));

Answer 4

我们可以使用Array.reduce 来计算总和，其中acc 是累加总和，各个对象被解构为age 变量，然后通过总和除以数组长度来计算平均值：

var people = [
  {
    name: 'Anna',
    age: 22
  },
  {
    name: 'Tom',
    age: 34
  }, {
    name: 'John',
    age: 12
  },
];

function getAvg(arr){
 return (people.reduce((acc, {age}) => (acc + age), 0))/arr.length;
}
console.log(getAvg(people));

我们还可以将函数映射到age 属性，并通过将数组连接成一个字符串并在Function 构造函数中对其求值来计算总和：

var people = [
  {
    name: 'Anna',
    age: 22
  },
  {
    name: 'Tom',
    age: 34
  }, {
    name: 'John',
    age: 12
  },
];

function getAvg(arr){
 return (new Function(`return ${people.map(({age}) => age).join("+")}`)()) / arr.length;
}
console.log(getAvg(people));

Answer 5

更简化的代码

只需使用您的代码执行 getAverage(people.map(p=> p.age));

var people = [
  {
    name: 'Anna',
    age: 22
  },
  {
    name: 'Tom',
    age: 34
  }, {
    name: 'John',
    age: 12
  },
];

let getAverage = arr => {
  let reducer = (total, currentValue) => total + currentValue;
  let sum = arr.reduce(reducer)
  return sum / arr.length;
};

console.log(getAverage(people.map(p=> p.age)));