我有这个对象数组,其中我有另一个对象数组:
[
{
id: 1,
country: [
{
id: "5a60626f1d41c80c8d3f8a85"
},
{
id: "5a6062661d41c80c8b2f0413"
}
]
},
{
id: 2,
country: [
{
id: "5a60626f1d41c80c8d3f8a83"
},
{
id: "5a60626f1d41c80c8d3f8a84"
}
]
}
];
如何获得
country
的平面数组,如下所示:
[
{ id: "5a60626f1d41c80c8d3f8a85" },
{ id: "5a6062661d41c80c8b2f0413" },
{ id: "5a60626f1d41c80c8d3f8a83" },
{ id: "5a60626f1d41c80c8d3f8a84" }
];
不使用
forEach
和临时变量?
当我这样做时:
(data || []).map(o=>{
return o.country.map(o2=>({id: o2.id}))
})
我得到了相同的结构。
Array.prototype.flat
和 Array.prototype.flatMap
const data=[{id:1,country:[{id:"5a60626f1d41c80c8d3f8a85"},{id:"5a6062661d41c80c8b2f0413"}]},{id:2,country:[{id:"5a60626f1d41c80c8d3f8a83"},{id:"5a60626f1d41c80c8d3f8a84"}]}];
console.log(
data.flatMap(
(elem) => elem.country
)
)
不需要任何 ES6 魔法,你可以通过连接内部
country
数组来减少数组。
const data=[{id:1,country:[{id:"5a60626f1d41c80c8d3f8a85"},{id:"5a6062661d41c80c8b2f0413"}]},{id:2,country:[{id:"5a60626f1d41c80c8d3f8a83"},{id:"5a60626f1d41c80c8d3f8a84"}]}];
console.log(
data.reduce(
(arr, elem) => arr.concat(elem.country), []
)
)
如果您想要 ES6 功能(箭头函数除外),请使用数组展开而不是 concat 方法:
const data=[{id:1,country:[{id:"5a60626f1d41c80c8d3f8a85"},{id:"5a6062661d41c80c8b2f0413"}]},{id:2,country:[{id:"5a60626f1d41c80c8d3f8a83"},{id:"5a60626f1d41c80c8d3f8a84"}]}];
console.log(
data.reduce(
(arr, elem) => [...arr, ...elem.country], []
)
)
注意:这些建议将在每次迭代时创建一个新数组。
为了效率,就必须牺牲一些优雅:
const data=[{id:1,country:[{id:"5a60626f1d41c80c8d3f8a85"},{id:"5a6062661d41c80c8b2f0413"}]},{id:2,country:[{id:"5a60626f1d41c80c8d3f8a83"},{id:"5a60626f1d41c80c8d3f8a84"}]}];
console.log(
data.reduce(
(arr, elem) => {
for (const c of elem.country) {
arr.push(c);
}
return arr;
}, []
)
)
const raw = [
{
id: 1,
country: [
{
id: "5a60626f1d41c80c8d3f8a85"
},
{
id: "5a6062661d41c80c8b2f0413"
}
]
},
{
id: 2,
country: [
{
id: "5a60626f1d41c80c8d3f8a83"
},
{
id: "5a60626f1d41c80c8d3f8a84"
}
]
}
];
const countryIds = raw
.map(x => x.country)
.reduce((acc, curr) => {
return [
...acc,
...curr.map(x => x.id)
];
}, []);
console.log(countryIds)
这可行,只需连接解决方案返回的嵌套数组即可
let arr = [{ "id": 1,
"country": [{
"id": "5a60626f1d41c80c8d3f8a85",
},
{
"id": "5a6062661d41c80c8b2f0413",
}
]
},
{
"id": 2,
"country": [{
"id": "5a60626f1d41c80c8d3f8a83",
},
{
"id": "5a60626f1d41c80c8d3f8a84",
}
]
}
];
//If you want an array of country objects
console.log([].concat.apply(...(arr || []).map(o=> o.country)))
//If you can an array od country ids
console.log([].concat.apply(...(arr || []).map(o=> o.country.map(country => country.id))))
Ayush Gupta 的解决方案适用于这种情况。但我想提供其他解决方案。
const arr = [
{
id: 1,
country: [
{
id: '5a60626f1d41c80c8d3f8a85'
},
{
id: '5a6062661d41c80c8b2f0413'
}
]
},
{
id: 2,
country: [
{
id: '5a60626f1d41c80c8d3f8a83'
},
{
id: '5a60626f1d41c80c8d3f8a84'
}
]
}
];
const ids = arr.reduce(
(acc, {country}) => [
...acc,
...country.map(({id}) => ({
id
}))
],
[]
);
console.log(ids);
对于 JSON 字符串数据,也可以在解析过程中完成:
var ids = [], json = '[{"id":1,"country":[{"id":"5a60626f1d41c80c8d3f8a85"},{"id":"5a6062661d41c80c8b2f0413"}]},{"id":2,"country":[{"id":"5a60626f1d41c80c8d3f8a83"},{"id":"5a60626f1d41c80c8d3f8a84"}]}]';
JSON.parse(json, (k, v) => v.big && ids.push(v));
console.log( ids );
我不确定为什么没有人提到
flat()
(可能对于大型数组,它的性能可能会较差)
const data = [
{
id: 1,
country: [
{
id: "5a60626f1d41c80c8d3f8a85"
},
{
id: "5a6062661d41c80c8b2f0413"
}
]
},
{
id: 2,
country: [
{
id: "5a60626f1d41c80c8d3f8a83"
},
{
id: "5a60626f1d41c80c8d3f8a84"
}
]
}
];
const transformed = (data || []).map(o=>{
return o.country.map(o2=>({id: o2.id}))
}).flat()
console.log(transformed)