Question

我目前正在尝试映射和缩小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
      }
    ]
  },
 ......
]

我知道为了按照排序编号进行map-reduce我可以使用：

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

但是，我希望按月减少排序编号我将不胜感激任何帮助。

谢谢，
杰

Answer 1

使用Array＃map获取data属性数组的数组，然后使用Array#concat和spread展平。使用Array#reduce将值收集到Map，然后使用Map#values和扩展语法转换回数组：

＆＃13;

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);

＆＃13;

这是一个无散布的版本：

＆＃13;

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);

＆＃13;

Answer 2

您可以使用reduce或concat (see Ori's answer)来获取展平的数据数组。从那里重新分配您的年份标签作为关键和重量作为价值。然后传递给另一个减速器，以便按月计算你的重量。

SELECT min(id) as id,manager,company,city 
FROM DistinctResult
group by company,city;

减少多维数组

2 个答案: