var arr = [
{city: "上海", location: "浦东"},
{city: "上海", location: "静安"},
{city: "北京", location: "内环"},
{city: "北京", location: "五环"},
{city: "苏州", location: "苏州"},
];
arr按city分组的方法,谢谢!
返回一个数组
[
{city:"",location:[]}
]
// 获取 {} 结构
const mapCityLoction = function(arr) {
let cities = {};
arr.forEach((address, index) => {
let locations = cities[address.city] || [];
locations.push(address.location);
cities[address.city] = locations;
})
return cities;
}
// forEach 获取 [ {city: , location}] 结构
const mapCityLoction_new = function() {
let newArr = [];
arr.forEach((address, i) => {
let index = -1;
let alreadyExists = newArr.some((newAddress, j) => {
if (address.city === newAddress.city) {
index = j;
return true;
}
});
if (!alreadyExists) {
newArr.push({
city: address.city,
location: [address.location]
});
} else {
newArr[index].location.push(address.location);
}
});
return newArr;
};
// reduce 获取 [ {city: , location}] 结构
const mapCityLoction_lastest = function() {
return arr.reduce( (prev, current) => {
let index = -1;
prev.some((address, i) => {
if (address.city === current.city) {
index = i;
return true;
}
});
if (index > -1) {
prev[index].location.push(current.location);
} else {
prev.push({
city: current.city,
location: [current.location]
});
}
return prev;
}, [])
};
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