JS合并数组对象中重复数据

别人的问题，想着不难，自己敲一下...没想到啊没想到...一个小小的数组重组数据，搞了两个小时.....

还是水平太差了...是水平太差了...水平太差了...平太差了...太差了...差了...了...

源数据：

目标数据：

// 源数据
var oldData = [
  {
    city_id: 1,
    city_name: '北京',
    city_img: "http://dfknbdjknvkjsfnvlkjdn.png",
    city_country: "中国"
  },
  {
    city_id: 2,
    city_name: '上海',
    city_img: "http://wergerbe.png",
    city_country: "中国"
  },
  {
    city_id: 3,
    city_name: '广州',
    city_img: "http://hrthhr.png",
    city_country: "中国"
  },
  {
    city_id: 4,
    city_name: '西雅图',
    city_img: "http://frevfd.png",
    city_country: "美国"
  },
  {
    city_id: 5,
    city_name: '纽约',
    city_img: "http://反而个.png",
    city_country: "美国"
  }
]

// 把源数据先变成目标数据的规则
var oldDataRule = []
oldData.forEach(el => {
  var oldObj = {
    name: el.city_country,
    citys:[]
  }
  var cityObj = {
    city_name: el.city_name,
    city_img: el.city_img,
    city_id: el.city_id
  }
  oldObj.citys.push(cityObj)
  oldDataRule.push(oldObj)
})

/**
 * 先去重，后合并
 * 1、源数据去重
 * 2、把去重后的数据和源数据中相同name的数据合并citys
*/
var newData = []
var newObj = {}
oldDataRule.forEach((el, i) => {
  if (!newObj[el.name]) {
    newData.push(el);
    newObj[el.name] = true;
  } else {
    newData.forEach(el => {
      if (el.name === oldDataRule[i].name) {
        el.citys = el.citys.concat(oldDataRule[i].citys);
        // el.citys = [...el.citys, ...oldDataRule[i].citys]; // es6语法
      }
    })
  }
})
console.log(newData); // 目标数据

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结果：