ES6 按数组中的对象属性求和

Question

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，我想计算2015-12-04 00:01:00. 此日期在以下数据中出现了 2 次，其值为5和6，将是：

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

我试过，arr = results.map(x => x.unit).reduce((a,c) => a + c)但它只返回一个值，而不是一个数组。

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

Answer 1

您可以将数据缩减为字典，然后将其映射到数组，如下所示

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
  }
]
*/