只获取对象的对象的一些键

Question

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,
    "c": 3,
  },
  "2020": {
    "a": 2,
    "c": 6,
  },
  "2021": {
    "a": 10,
    "c": 12,
  }
}

const obj2 = {
  "2019": {
    "b": 2,
    "d": 4
  },
  "2020": {
    "b": 4,
    "d": 8
  },
  "2021": {
    "b": 11,
    "d": 13
  }
}

因此根据内部对象的一些键将对象“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 } }
]

差不多了，但还不完美。哪种方法更好？

Answer 1

您可以结合使用 map、reduce 方法和一个 for...in 循环，将键数组转换为对象数组。然后你可以使用数组解构来得到两个独立的对象。

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)

Answer 2

问题是 map return 是一个包含替换元素的数组，而您需要一个对象。

由于您已经在使用 Lodash，因此您可以使用 mapValues 来转换对象的值，并 return 使用对象而不是数组。

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

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

Answer 3

您可以使用给定对象的条目映射所需的键。

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', 'c'], ['b', '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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Answer 4

下一个提供的示例代码是基于 reduce 的，通用但在其用法中可配置...

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,
    "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 [

  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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只获取对象的对象的一些键

Get only some keys of object of objects

javascript

mapping

reduce

data-structures