仅获取对象的某些键

问题描述

我有这个对象：

const dataset = {
  "2019": {
    "a": 1,"b": 2,"c": 3,"d": 4
  },"2020": {
    "a": 2,"b": 4,"c": 6,"d": 8
  },"2021": {
    "a": 10,"b": 11,"c": 12,"d": 13
  }
}

我想获得这两个对象：

const obj1 = {
  "2019": {
    "a": 1,},}
}

const obj2 = {
  "2019": {
    "b": 2,"2020": {
    "b": 4,"2021": {
    "b": 11,"d": 13
  }
}

因此，根据内部对象的某些键将对象“拆分”为两个对象。 这是我尝试过的：

function pickKeys(dataObj,keys) {
  return Object.entries(dataObj).map(([d,obj]) => {
  return { [d]: _.pick(obj,keys) }
})
}
const obj1 = pickKeys(dataset,['a','c'])

结果是：

const obj1 = [
  { '2019': { a: 1,c: 3 } },{ '2020': { a: 2,c: 6 } },{ '2021': { a: 10,c: 12 } }
]

所以几乎在那里，但这并不完美。哪种方法更好？

解决方法

您可以使用map，reduce方法和一个for...in循环的组合来执行此操作，该循环会将键数组转换为对象数组。然后，您可以使用数组解构来获取两个单独的对象。

const dataset = {"2019":{"a":1,"b":2,"c":3,"d":4},"2020":{"a":2,"b":4,"c":6,"d":8},"2021":{"a":10,"b":11,"c":12,"d":13}}

const [a,b] = [['a','c'],['b','d']]
.map(keys => keys.reduce((r,key) => {
  for (let year in dataset) {
    if (!r[year]) r[year] = {}
    r[year][key] = dataset[year][key]
  }

  return r;
},{}))

console.log(a)
console.log(b)

,

问题是map返回一个带有替换元素的数组，而您需要一个对象。

由于您已经在使用Lodash，因此可以使用mapValues来转换对象的值并返回对象而不是数组。

function pickKeys(dataObj,keys) {
  return _.mapValues(dataObj,obj => _.pick(obj,keys));
}

function pickKeys(dataObj,keys));
}

const dataset = {
  "2019": {
    "a": 1,"b": 2,"c": 3,"d": 4
  },"2020": {
    "a": 2,"b": 4,"c": 6,"d": 8
  },"2021": {
    "a": 10,"b": 11,"c": 12,"d": 13
  }
}

console.log(pickKeys(dataset,["a","c"]));

<script src="https://cdn.jsdelivr.net/npm/lodash@4.17.15/lodash.min.js"></script>

,

您可以使用给定对象的条目来映射所需的键。

const
    dataset = { 2019: { a: 1,b: 2,c: 3,d: 4 },2020: { a: 2,b: 4,c: 6,d: 8 },2021: { a: 10,b: 11,c: 12,d: 13 } },groups = [['a','d']],[result1,result2] = Object
        .entries(dataset)
        .reduce((r,[k,o]) =>
            groups.map((group,i) =>
                group.reduce(
                    (q,g) => ({ ...q,[k]: { ...q[k],[g]: o[g] } }),r[i] || {}
                )
            ),[]
        );

console.log(result1);
console.log(result2);

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,

下一个提供的示例代码基于reduce，是通用的，但其用法可以配置...

function createAndCollectSubdata(collector,dataEntry) {

  const { keyLists,subdataList } = collector;
  const [ dataKey,dataValue ] = dataEntry;

  keyLists.forEach((keyList,idx) => {

    const data = subdataList[idx] || (subdataList[idx] = {});
    const subdata = data[dataKey] || (data[dataKey] = {}) ;

    keyList.forEach(key => subdata[key] = dataValue[key]);
  });
  return collector;
}

const dataset = {
  "2019": {
    "a": 1,"d": 13
  }
};
const [

  acSubdata,bdSubdata
  
] = Object.entries(dataset).reduce(createAndCollectSubdata,{

  keyLists: [["a","c"],["b","d"]],subdataList: []

}).subdataList;

console.log('acSubdata :',acSubdata);
console.log('bdSubdata :',bdSubdata);

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