合并嵌套 arrays 的最佳方法是什么

Question

I have an array of objects that looks like this:

[
 {external_id: 1, items: [{k: 'v'}] },
 {external_id: 2, items: [{k1: 'v1'}] },
 {external_id: 1, items: [{k2: 'v2'}, {k3: 'v3'}] }
]

What I want to do is merge nested arrays based on external_id and return 'clean array' which will look like this:

[
 {external_id: 1, items: [{k: 'v'}, {k2: 'v2'}, {k3: 'v3'}] },
 {external_id: 2, items: [{k1: 'v1'}] }
]

So my question is what is the clean way to achieve that without using classic for-loop?

Answer 1

Using reduce and sort

 let data = [{ external_id: 1, items: [{ k: 'v' }] }, { external_id: 2, items: [{ k1: 'v1' }] }, { external_id: 1, items: [{ k2: 'v2' }, { k3: 'v3' }] }, ]; let ans = data.sort(function(a, b) { return a['external_id'] - b['external_id']; }).reduce((acc, currentObject) => { const endObject = acc[acc.length - 1]; if (endObject && endObject['external_id'] === currentObject.external_id) { endObject.items.push(...currentObject.items); } else { acc.push({...currentObject }); } return acc; }, []); console.log(ans);

Answer 2

You will have to loop. You can choose to loop with for , forEach , map , reduce , find , ...etc, but you'll have to loop.

Here is a way that creates a Map keyed by the external_id, and then populates that map with the items. Finally the values of that map represent the result:

 let data = [{external_id: 1, items: [{k: 'v'}] },{external_id: 2, items: [{k1: 'v1'}] },{external_id: 1, items: [{k2: 'v2'}, {k3: 'v3'}] }]; let map = new Map(data.map(({external_id}) => [external_id, { external_id, items:[] }])); data.forEach(o => map.get(o.external_id).items.push(...o.items)); let result = [...map.values()]; console.log(result);

Answer 3

using another object to group objects with same external_id property

let a = [
    {external_id: 1, items: [{k: 'v'}] },
    {external_id: 2, items: [{k1: 'v1'}] },
    {external_id: 1, items: [{k2: 'v2'}, {k3: 'v3'}] }
]

let obj = {};

a.forEach( ({external_id, items}) => {
    obj[external_id] ??= new Set;
    items.map( i => {
        obj[external_id].add(JSON.stringify(i));
    });
});

a = Object.keys(obj).map( (n) => {
    n = Number(n);
    return {
        external_id:n,
        items: [...obj[n]].map(JSON.parse)
    }
})