降维阵列

Question

目前，我正试图映射和减少函数，以使多维数组变得平坦。

这是一个模拟示例数据集：

data: [
  {
    label: "Sort-01"
    data: [
      {
        label: "OCT-2017"
        weight: 2304
      },
      {
        label: "NOV-2017"
        weight: 1783
      }
    ]
  },
  {
    label: "Sort-02"
    data: [
      {
        label: "OCT-2017"
        weight: 4785
      },
      {
        label: "NOV-2017"
        weight: 102
      }
    ]
  },
 ......
]

我知道，为了映射-按排序编号减少，我可以使用：

data.map(sort => sort.data.reduce((a,b) => a.weight + b.weight));

但是，我想按月减少，而不是排序。

我很感谢你的帮助。

谢谢,

杰伦

Answer 1

使用Array#map获取data属性数组的a数组，然后与Array#concat和铺展一起扁平。使用Array#reduce将值收集到地图中，然后使用Map#values，并使用spread语法将其转换回数组：

​

const array = [{"label":"Sort-01","data":[{"label":"OCT-2017","weight":2304},{"label":"NOV-2017","weight":1783}]},{"label":"Sort-02","data":[{"label":"OCT-2017","weight":4785},{"label":"NOV-2017","weight":102}]}];

const result = [... // spread the values iterator to an array
  [].concat(...array.map(({ data }) => data)) // map the array into an array of data arrays
  .reduce((m, { label, weight }) => {
    // take item if label exists in map, if not create new
    const item = m.get(label) || { label, weight: 0 };
    
    item.weight += weight; // add the weight
  
    return m.set(label, item); // set the item in the map
  }, new Map).values()] // get the values iterator

console.log(result);

​

下面是一个无扩展的版本：

​

const array = [{"label":"Sort-01","data":[{"label":"OCT-2017","weight":2304},{"label":"NOV-2017","weight":1783}]},{"label":"Sort-02","data":[{"label":"OCT-2017","weight":4785},{"label":"NOV-2017","weight":102}]}];

const helper = Object.create(null);
const result = [].concat.apply([], array.map(({ data }) => data)) // map the array into an array of data arrays, and flatten by apply concat
  .reduce((r, { label, weight }) => {
    // if label is not in helper, add to helper, and push to r
    if(!helper[label]) {
      helper[label] = { label, weight: 0 };
      r.push(helper[label]);
    }
    
    helper[label].weight += weight; // add the weight to the object
  
    return r;
  }, []) // get the values iterator

console.log(result);

​

Answer 2

您可以使用reduce或(见Ori的答复)来获得扁平的数据数组。从那里重新分配你的年份标签作为关键和重量作为价值。然后转到另一个减速机，以便按月将你的重量加起来。

​

const data = [{label: "Sort-01",data: [{label: "OCT-2017",weight: 2304,},{label: "NOV-2017",weight: 1783,},],},{label: "Sort-02",data: [{label: "OCT-2017",weight: 4785,},{label: "NOV-2017",weight: 102,},],},];
const flatten = (acc, cur) => { 
  cur.data.forEach(val => acc.push(val)); 
  return acc;
};
const monthMap = ({ label, weight }) => ({ [label]: weight });
const reducer = (acc, cur) => {
  const key = Object.keys(cur)[0]
  if (!acc.hasOwnProperty(key)) { acc[key] = 0 }
  acc[key] += cur[key];
  return acc;
};

let x = data.reduce(flatten, []).map(monthMap).reduce(reducer, {});
console.log(x);

​