将以前的日期值与今天的日期相加答案

【问题标题】：Sum previous date values to today Date将以前的日期值与今天的日期相加
【发布时间】：2021-07-04 16:29:55
【问题描述】：

我想计算以前的日期值到当前日期等等。这是我的脚本。

我已经为初始 prevDayStock 获取了前一天的股票价值，即 let prevStock = 21

let prevStock = 21; 
let stocksArr= [
  { date: '2021-06-30',stock: 4 },
  { date: '2021-07-01',stock: 5 },
  { date: '2021-07-02',stock: 2 },
  { date: '2021-07-03',stock: 1 },
  { date: '2021-07-04', stock: 5 },
  { date: '2021-07-05',stock: 3 },
  { date: '2021-07-06', stock: 4 },
  { date: '2021-07-07',stock: 1 },
  { date: '2021-07-08', stock: 4 }
]

stocksArr.reduce((acc, cur, idx, arr) => {
  const prod = idx === 0 ? 0 : arr[idx - 1].stock;
  const value = acc + cur.stock + prod;
  cur.stock = acc;
  return value;
}, prevStock); 
  console.log(stocksArr)

预期结果：

    [{ date: '2021-06-30',stock: 21 },
      { date: '2021-07-01',stock: 24 },
      { date: '2021-07-02',stock: 29 },
      { date: '2021-07-03',stock: 31 },
      { date: '2021-07-04', stock: 32 },
      { date: '2021-07-05',stock: 37 },
      { date: '2021-07-06', stock: 40 },
      { date: '2021-07-07',stock: 44 },
      { date: '2021-07-08', stock: 45 }]

什么是正确的解决方案。

let prevStock = 21;
let stocksArr= [
  { date: '2021-06-30',stock: 4 },
  { date: '2021-07-01',stock: 5 },
  { date: '2021-07-02',stock: 2 },
  { date: '2021-07-03',stock: 1 },
  { date: '2021-07-04', stock: 5 },
  { date: '2021-07-05',stock: 3 },
  { date: '2021-07-06', stock: 4 },
  { date: '2021-07-07',stock: 1 },
  { date: '2021-07-08', stock: 4 }
]

stocksArr.reduce((acc, cur, idx, arr) => {
  const prod = idx === 0 ? 0 : arr[idx - 1].stock;
  const value = acc + cur.stock + prod;
  cur.stock = acc;
  return value;
}, prevStock); 
  console.log(stocksArr)

【问题讨论】：

标签： javascript object ecmascript-6

【解决方案1】：

如果你想要累积结果，这里就是答案

    var stocksArr= [
      { date: '2021-06-30',stock: 4 },
      { date: '2021-07-01',stock: 5 },
      { date: '2021-07-02',stock: 2 },
      { date: '2021-07-03',stock: 1 },
      { date: '2021-07-04', stock: 5 },
      { date: '2021-07-05',stock: 3 },
      { date: '2021-07-06', stock: 4 },
      { date: '2021-07-07',stock: 1 },
      { date: '2021-07-08', stock: 4 }
    ]
    
var result = stocksArr.reduce(function(r, a) {
  if (r.length > 0)
    a.stock += r[r.length - 1];
  r.push(a.stock);
  a['sum'] = a.stock
  return r;
}, [21]); // <-- pass intialValue to here

    
    console.log(stocksArr)

    [
  {
    "date": "2021-06-30",
    "stock": 25,
    "sum": 25
  },
  {
    "date": "2021-07-01",
    "stock": 30,
    "sum": 30
  },
  {
    "date": "2021-07-02",
    "stock": 32,
    "sum": 32
  },
  {
    "date": "2021-07-03",
    "stock": 33,
    "sum": 33
  },
  {
    "date": "2021-07-04",
    "stock": 38,
    "sum": 38
  },
  {
    "date": "2021-07-05",
    "stock": 41,
    "sum": 41
  },
  {
    "date": "2021-07-06",
    "stock": 45,
    "sum": 45
  },
  {
    "date": "2021-07-07",
    "stock": 46,
    "sum": 46
  },
  {
    "date": "2021-07-08",
    "stock": 50,
    "sum": 50
  }
]

【讨论】：

感谢您的回答。相同的累积值应放在各自的日期。
SO 期望返回相同的对象数组。当你减少时注意，原始对象数组没有变异
@mplungjan 它必须采用我的初始化值 let prevStock = 21;
@underscore a= a.stock;这将代替 `a["sum"] = a.stock. I want notify you that my initial value is let prevStock = 21;` 它必须考虑第一个结果
@Jay 请检查更新后的代码。您可以在回调后简单地将 intialValue 传递给 reducer 函数