减少多维数组

Question

我目前正在尝试映射和缩减函数以展平多维数组。
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
      }
    ]
  },
 ......
]

我知道为了按排序编号进行 map-reduce，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数。
我将不胜感激任何帮助。

谢谢，
周杰伦

Answer 1

使用 Array#map 获取 data 属性数组的数组，然后用 Array#concat and spread. Use Array#reduce to collect the values into a Map, then use Map#values 展平，然后使用扩展语法转换回数组：

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);

这是一个无传播版本：

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 或来获得扁平化的数据数组。从那里将您的年份标签重新分配为键，将权重重新分配为值。然后传递给另一个减速器，以便按月计算总重量。

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);

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