ES6数组中按对象属性求和 [英] ES6 Sum by object property in an array

问题描述

我试图按日期对单位值求和，并创建一个没有重复日期的新数组.例如，我要计算 2015-12-04 00:01:00 的总数.此日期在以下数据中发生了2次，其值为 5 和 6 ，该值将为:

I am trying to sum the unit value by date, and create a new array where there are no duplicate dates. For example, I want to calculate the total of 2015-12-04 00:01:00. This date has occurred 2 times in the following data, its value is 5 and 6, which is going to be:

[{date: '2015-12-04 00:01:00', unit: 11}, ... etc]

我尝试了 arr = results.map(x => x.unit).reduce((a，c)=> a + c)，但它只返回一个值，不是数组.

I have tried arr = results.map(x => x.unit).reduce((a,c) => a + c) but it only return a single value, not an array.

results = [ { unit: 5, date: '2015-12-04 00:01:00' },
          { unit: 10, date: '2015-12-04 00:01:00' },
          { unit: 5, date: '2015-12-04 00:31:00' },
          { unit: 9, date: '2015-12-04 00:31:00' },
          { unit: 5, date: '2015-12-04 01:01:00' },
          { unit: 10, date: '2015-12-04 01:01:00' },
          { unit: 10, date: '2015-12-04 01:31:00' },
          { unit: 5, date: '2015-12-04 01:31:00' },
          { unit: 10, date: '2015-12-04 02:01:00' },
          { unit: 5, date: '2015-12-04 02:01:00' },
          { unit: 5, date: '2015-12-04 02:31:00' },
          { unit: 9, date: '2015-12-04 02:31:00' },
          { unit: 5, date: '2015-12-04 03:01:00' },
          { unit: 9, date: '2015-12-04 03:01:00' },
          { unit: 5, date: '2015-12-04 03:31:00' },
          { unit: 10, date: '2015-12-04 03:31:00' },
          { unit: 10, date: '2015-12-04 04:01:00' },
          { unit: 5, date: '2015-12-04 04:01:00' }];

arr = results.map(x => x.unit).reduce((a,c) => a + c);
console.log(arr);

推荐答案

您可以将数据精简为字典，然后将其映射到数组，像这样

You can reduce your data to a dictionary and then map it to an array like so

results = [ { unit: 5, date: '2015-12-04 00:01:00' },
      { unit: 10, date: '2015-12-04 00:01:00' },
      { unit: 5, date: '2015-12-04 00:31:00' },
      { unit: 9, date: '2015-12-04 00:31:00' },
      { unit: 5, date: '2015-12-04 01:01:00' },
      { unit: 10, date: '2015-12-04 01:01:00' },
      { unit: 10, date: '2015-12-04 01:31:00' },
      { unit: 5, date: '2015-12-04 01:31:00' },
      { unit: 10, date: '2015-12-04 02:01:00' },
      { unit: 5, date: '2015-12-04 02:01:00' },
      { unit: 5, date: '2015-12-04 02:31:00' },
      { unit: 9, date: '2015-12-04 02:31:00' },
      { unit: 5, date: '2015-12-04 03:01:00' },
      { unit: 9, date: '2015-12-04 03:01:00' },
      { unit: 5, date: '2015-12-04 03:31:00' },
      { unit: 10, date: '2015-12-04 03:31:00' },
      { unit: 10, date: '2015-12-04 04:01:00' },
      { unit: 5, date: '2015-12-04 04:01:00' }]

// first make an object with {date: unit} value as such
const newResults = results.reduce((acc, item) => ({
  ...acc,
  [item.date]: (acc[item.date] || 0) + item.unit
}) , {})

console.log(newResults)
/*
{
  "2015-12-04 00:01:00": 15,
  "2015-12-04 00:31:00": 14,
  "2015-12-04 01:01:00": 15,
  "2015-12-04 01:31:00": 15,
  "2015-12-04 02:01:00": 15,
  "2015-12-04 02:31:00": 14,
  "2015-12-04 03:01:00": 14,
  "2015-12-04 03:31:00": 15,
  "2015-12-04 04:01:00": 15
}
*/

// now if you want array representation for this you can do

const finalResult = Object.keys(newResults).map(key => ({date: key, unit: newResults[key]}))

console.log(finalResult)
/*
[
  {
    "date": "2015-12-04 00:01:00",
    "unit": 15
  },
  {
    "date": "2015-12-04 00:31:00",
    "unit": 14
  },
  {
    "date": "2015-12-04 01:01:00",
    "unit": 15
  },
  {
    "date": "2015-12-04 01:31:00",
    "unit": 15
  },
  {
    "date": "2015-12-04 02:01:00",
    "unit": 15
  },
  {
    "date": "2015-12-04 02:31:00",
    "unit": 14
  },
  {
    "date": "2015-12-04 03:01:00",
    "unit": 14
  },
  {
    "date": "2015-12-04 03:31:00",
    "unit": 15
  },
  {
    "date": "2015-12-04 04:01:00",
    "unit": 15
  }
]
*/

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