数组中分组项和计数项的简洁方法 [英] Concise way to Group by and Count item in array

问题描述

我有一个像这样的数组:

const arr = [ {name: 'Server 1', country: 'DE'}, {name: 'Server 2', country: 'PL'}, 
              {name: 'Server 3', country: 'US'}, {name: 'Server 4', country: 'DE'}, 
              {name: 'Server 5', country: 'US'}];

我想要的是 group and count 以获得如下的输出:

What I want is group and count to get the ouput like below:

 [
  {
    "country": "DE",
    "count": 2
  },
  {
    "country": "PL",
    "count": 1
  },
  {
    "country": "US",
    "count": 2
  }
]

当前，我正在使用 lodash ，但是我认为有更好的方法(例如，使用 _groupBy 或类似的方法)来解决它，对吧?

Currently, I'm using lodash but I think there are better ways (for example, using _groupBy or something like that) to resolve it, right?

我的代码在这里:

const arr = [ {name: 'Server 1', country: 'DE'}, {name: 'Server 2', country: 'PL'}, {name: 'Server 3', country: 'US'}, {name: 'Server 4', country: 'DE'}, {name: 'Server 5', country: 'US'}];

const objectGroupby = _.countBy(arr, 'country');
const result = Object.entries(objectGroupby).map(([key, value]) => ({country: key, count: value}));
console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.21/lodash.min.js"></script>

如您所见， _.countBy(arr，'country')只是返回一个对象而不是数组.

As you can see, _.countBy(arr, 'country') just returns an object instead of an array.

{
  "DE": 2,
  "PL": 1,
  "US": 2
}

然后我必须使用 Object.entries()& map 来解决它.

Then I have to use Object.entries() & map to resolve it.

推荐答案

万岁!!!

最近几天研究之后，我终于像这样使用 groupBy 找出了解决方案.

After researching in recent days, I finally figure out the solution using groupBy like this.

const arr = [ {name: 'Server 1', country: 'DE'}, {name: 'Server 2', country: 'PL'}, {name: 'Server 3', country: 'US'}, {name: 'Server 4', country: 'DE'}, {name: 'Server 5', country: 'US'}];
const result = _(arr).groupBy(x => x.country)
                     .map((value, key) => ({country: key, count: value.length})); 
console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.21/lodash.min.js"></script>

说明:

1. 第1步:根据 country 属性
对数组元素进行分组
2. 第2步:使用具有2个参数值的.map: key 是组的名称(国家/地区)， value 是对象的数组.

1. Step 1: Group the elements of array-based on country property
2. Step 2: Using .map with 2 params value: key is the group's name (country), value is the array of objects.

参考资源:

• 使用lodash .groupBy.如何为分组输出添加自己的键?

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