Lodash-按数组中的位置排序

Question

I have an array of objects

let myArray = [
    {
        id: 'first',
        name: 'john',
    },
    {
        id: 'second',
        name: 'Emmy',
    },
    {
        id: 'third',
        name: 'Lazarus',
    }
]

and an array

let sorter = ['second', 'third', 'first']

I would like to use lodash sorting method to sort my objects according to their position in sorter . So that the output would be

let mySortedArray = [
    {
        id: 'second',
        name: 'Emmy',
    },
    {
        id: 'third',
        name: 'Lazarus',
    },
    {
        id: 'first',
        name: 'john',
    }
]

Is it possible to do so?

Answer 1

You can achieve this by using map and find :

 let myArray = [ { id: "first", name: "john" }, { id: "second", name: "Emmy" }, { id: "third", name: "Lazarus" } ]; let sorter = ["second", "third", "first"]; let mySortedArray = sorter.map(x => myArray.find(y => y.id === x)); console.log(mySortedArray); 

Answer 2

Using lodash you can use _.sortBy

 let myArray = [ { id: 'first', name: 'john', }, { id: 'second', name: 'Emmy', }, { id: 'third', name: 'Lazarus', } ] let sorter = ['second', 'third', 'first'] console.log(_.sortBy(myArray,(i) => {return sorter.indexOf(i.id)})) 

 .as-console-wrapper { max-height: 100% !important; top: 0; } 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/2.4.1/lodash.min.js"></script> 

Answer 3

If you want to sort the array in-place, you don't need Lodash, you can easily do it with vanilla JavaScript

 let myArray = [ { id: 'first', name: 'john', }, { id: 'second', name: 'Emmy', }, { id: 'third', name: 'Lazarus', } ] let sorter = ['second', 'third', 'first'] //create a lookup table (map) to save looking through the array const sortLookup = new Map(); //populate with element as key - index as value sorter.forEach((id, index) => sortLookup.set(id, index)); //sort using the indexes of sorter myArray.sort((a, b) => sortLookup.get(a.id) - sortLookup.get(b.id)) console.log(myArray) 

This is using a Map but the same can easily be accomplished with a plain JavaScript Object {} . You don't even need to pre-compute the lookup myArray.sort((a, b) => sorter.indexOf(a.id) - sorter.indexOf(b.id)) would give the exact same output but it would mean that instead of traversing sorter once for a complexity of O(n) , you potentially have O(n^m) or O(n^n) (if both arrays are the same length)

Answer 4

Since you have an index array in the case of the sorter you can _.keyBy the main array and then use the sorter to access by index:

 let myArray = [ { id: 'first', name: 'john', }, { id: 'second', name: 'Emmy', }, { id: 'third', name: 'Lazarus', } ] let sorter = ['second', 'third', 'first'] const idMap = _.keyBy(myArray, 'id') const result = _.map(sorter, x => idMap[x]) console.log(result) 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script> 

This should perform better since you only do the idMap once and then access it by index .