如何在 JSON 数组中找到每个日期的最新时间？

如何解决如何在 JSON 数组中找到每个日期的最新时间？

我有这个 JSON 格式的数组：

var result=[
    {
        "index": 13,"id": 1122,

*

解决方法

以下方法：

• 从数组中获取仅包含日期的唯一列表，即 dd/mm/yyyy
• 对于唯一列表中的每个日期，根据该日期的时间创建一个排序数组
• 从该日期的排序数组中返回第 0 个项目

示例代码：

var result = [
  {
    "index": 13,"id": 1122,"price": 100,"dateTime": "11/12/2020 1:59"
  },{
    "index": 14,"price": 300,"dateTime": "11/12/2020 3:15"
  },{
    "index": 15,"price": 314,"dateTime": "11/13/2020 2:20"
  },{
    "index": 16,"price": 280,"dateTime": "11/13/2020 2:23"
  }
];

// get a list of the dates in result
// nothing fancy - the date is just a key
var dates = result.map(k => k.dateTime.substr(0,10));
// get unique dates from this array
var uniqueDates = Array.from(new Set(dates));
// for each unique date,sort the times descending
// return the first item (latest) for that date
var filtered = uniqueDates.map(ud => {
  var dateItems = result.filter(d => d.dateTime.substr(0,10) == ud);
  dateItems.sort((a,b) => (new Date(b.dateTime)).getTime() - (new Date(a.dateTime)).getTime());
  return dateItems[0];
});
// output
console.log(filtered);

,

根据 Date 的 dateTime 值对数组进行排序，写入一个仅以日期为键的结果数组，检索结果的值。

顺便说一下，TypeError 是因为您应该检查循环中的 i + 1 是否小于 result.length（对于其中的最后一个元素，这将是 falsy循环。在这种情况下，new Date(result[i+1].dateTime) 将抛出错误）。

// initialize log helper
const log = Logger();

// create an empty Object
const result = {};

// sort data ascending
const dataSorted = getData().sort((a,b) =>
  new Date(a.dateTime) - new Date(b.dateTime));

// add to result with datestring as key. 
// The value with the most recent date will be preserved
// because key values are unique (so equal keys are overwritten)
dataSorted.forEach(v => result[new Date(v.dateTime).toDateString()] = v);

// the values of [result] contain the most recent records per date
log(Object.values(result));

// this can also be a one liner,using a reducer method
const resultX = Object.values(
  getData()
    .sort( (a,b) => new Date(a.dateTime) - new Date(b.dateTime) )
    .reduce( (acc,value) => 
      ({...acc,[new Date(value.dateTime).toDateString()]: value}),{} )
);

log(`\n**from reducer`,resultX);

function getData() {
  return [{
      "index": 13,"dateTime": "11/12/2020 1:59"
    },{
      "index": 14,"dateTime": "11/12/2020 3:15"
    },{
      "index": 15,"dateTime": "11/13/2020 2:20"
    },{
      "index": 16,"dateTime": "11/13/2020 2:23"
    }
  ];
}

function Logger() {
  const report = document.querySelector("#report") || 
    document.body.insertAdjacentElement(
      "beforeend",Object.assign(document.createElement("pre"),{id: "report"}));
  return (...args) => args.forEach(stuff =>
      report.textContent += (stuff instanceof Object 
        ? JSON.stringify(stuff,null,2) : stuff) + "\n");
}

,

您可以根据日期对数据进行分组，例如

const groups = data.reduce((groups,currVal) => {
  const date = currVal.dateTime.split(' ')[0];
  if (!groups[date]) {
    groups[date] = [];
  }
  groups[date].push(currVal);
  return groups;
},{});

->这里我们用split(' ')分割日期和时间部分，单独取日期组成一个组，

const date = currVal.dateTime.split(' ')[0];

然后你可以使用该方法获取最近的日期和时间，

groups[item].reduce((a,b) => (a.dateTime > b.dateTime ? a : b));

工作片段：

const data = [
    {
        "index": 13,{
        "index": 14,{
        "index": 15,{
        "index": 16,"dateTime": "11/13/2020 2:23"
    }
];


//Group the data based on date
const groups = data.reduce((groups,{});

//Get the recent date and time based on each group
const result = [];
Object.keys(groups).filter(item => {
  const newData = groups[item].reduce((a,b) => (a.dateTime > b.dateTime ? a : b));
  result.push(newData);
});

console.log(result)