如何计算数组中同名对象的数量？答案

【问题标题】：How can I count the amount of objects with the same name in array?如何计算数组中同名对象的数量？
【发布时间】：2020-10-07 19:53:36
【问题描述】：

我有这个数组并试图获取具有相同name 属性的对象的计数。我怎样才能做到这一点？也许以现代“es6”方式

let cars = [
    {id: 1, name: 'Mercedes', year: '2015'},
    {id: 2, name: 'Mercedes', year: '2000'},
    {id: 3, name: 'BMW', year: '2010'},
    {id: 4, name: 'BMW', year: '2004'},
    {id: 5, name: 'Volvo', year: '2012'},
    {id: 6, name: 'Volvo', year: '2014'} 
];

【问题讨论】：

您可以考虑使用 Array.reduce 方法。见developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…
这能回答你的问题吗？ Counting occurrences of particular property value in array of objects

标签： javascript arrays object ecmascript-6

【解决方案1】：

let counterObj = {}

let cars = [
    {id: 1, name: 'Mercedes', year: '2015'},
    {id: 2, name: 'Mercedes', year: '2000'},
    {id: 3, name: 'BMW', year: '2010'},
    {id: 4, name: 'BMW', year: '2004'},
    {id: 5, name: 'Volvo', year: '2012'},
    {id: 6, name: 'Volvo', year: '2014'} 
];


for (property of cars){
    counterObj[property.name] = 1 + (counterObj[property.name] || 0)
}

console.log(counterObj)

这应该可以解决问题！

【讨论】：

【解决方案2】：

这里有一个解决方案：

let cars = [
  { id: 1, name: "Mercedes", year: "2015" },
  { id: 2, name: "Mercedes", year: "2000" },
  { id: 3, name: "BMW", year: "2010" },
  { id: 4, name: "BMW", year: "2004" },
  { id: 5, name: "Volvo", year: "2012" },
  { id: 6, name: "Volvo", year: "2014" },
];

let numbers = cars.reduce((acc, child) => {
  if (!acc[child.name]) {
    acc[child.name] = 0;
  }
  acc[child.name]++;
  return acc;
}, {});

console.log(numbers);

【讨论】：

【解决方案3】：

let cars = [
    {id: 1, name: 'Mercedes', year: '2015'},
    {id: 2, name: 'Mercedes', year: '2000'},
    {id: 3, name: 'BMW', year: '2010'},
    {id: 4, name: 'BMW', year: '2004'},
    {id: 5, name: 'Volvo', year: '2012'},
    {id: 6, name: 'Volvo', year: '2014'} 
];

let obj = {}

cars.forEach((item) => {
  console.log(obj[item.name])
  if (!obj[item.name]) {
    obj[item.name] = 1;
  } else {
    obj[item.name] += 1;
  }
})

console.log(obj)

【讨论】：

【解决方案4】：

您可以使用一个简单的reduce 函数，它会遍历每个对象并将计数加一

let cars = [
  { id: 1, name: "Mercedes", year: "2015" },
  { id: 2, name: "Mercedes", year: "2000" },
  { id: 3, name: "BMW", year: "2010" },
  { id: 4, name: "BMW", year: "2004" },
  { id: 5, name: "Volvo", year: "2012" },
  { id: 6, name: "Volvo", year: "2014" }
];

let count = cars.reduce((acc, child) => {
  acc[child.name] = (acc[child.name] || 0) + 1;
  return acc;
}, {});

console.log(count);

【讨论】：