javascript - 如何通过特定对象键对数组中的值求和？

Question

我有一个 js 对象数组，如下所示:

var objArr = [
     {"Country": "US", "City": "MyCity1", "2017-07-12": "1", "2017-07-13": "2"},
     {"Country": "US", "City": "MyCity2", "2017-07-12": "2", "2017-07-13": "2"},
     {"Country": "CN", "City": "MyCity1", "2017-07-12": "5", "2017-07-13": "7"},
     {"Country": "CN", "City": "MyCity2", "2017-07-12": "5", "2017-07-13": "7"}
   ]

我想创建一个新数组，其中国家是独一无二的，但日期也应该相加。

{"Country": "US", "2017-07-12":  "3", "2017-07-13": "4"},
{"Country": "CN", "2017-07-12": "10", "2017-07-13": "14"}
            ^^^^                ^^^^                ^^^^   

我很难理解它。
我必须先过滤，以某种方式减少它，重新映射它，......我不知道开始吗？
任何帮助将不胜感激，谢谢!

Answer 1

使用Array.reduce ，检查当前国家的对象是否存在，如果存在，循环遍历Object.keys要更新值，如果没有，请推送一个新值:

编辑 : 如果你不想要 City 你可以解构它 {City, ...curr}

var objArr = [
  { Country: "US", City: "MyCity1", "2017-07-12": "1", "2017-07-13": "2" },
  { Country: "US", City: "MyCity2", "2017-07-12": "2", "2017-07-13": "2" },
  { Country: "CN", City: "MyCity1", "2017-07-12": "5", "2017-07-13": "7" },
  { Country: "CN", City: "MyCity2", "2017-07-12": "5", "2017-07-13": "7" }
];

var result = objArr.reduce((acc, {City, ...curr}) => {
  const ndx = acc.findIndex(e => e.Country === curr.Country);
  if (ndx > -1) {
    const [country, ...keys] = Object.keys(curr);
    keys.forEach(k => {
      acc[ndx][k] = +acc[ndx][k] + +curr[k];
    });
  } else {
    acc.push(curr);
  }
  return acc;
}, []);

console.log(result);