CODEWITHSUNDEEP
javascriptarraysforeach
PCK
PCK

Reputation: 1444

Looping over two arrays in javascript simultaneously

let masterList=[{id:1,name:'Abc'},{id:2,name:'Def'},{id:3,name:'Ghi'}];
let selectedList=[2,3];

The desired result is to have 

//desiredList=[{id:2,name:'Def'},{id:3,name:'Ghi'}]

Currently what I am doing is

     let parsedArray = [];
      masterList.forEach(mItem => {
            selectedList.forEach(sItem => {
                if (mItem.id === sItem) {
                    parsedArray.push(mItem);
                }
            });
        });
     desiredList=parsedArray

I do not find this method efficient when iterating over large arrays, is there any logic, any inbuilt javascript operators using which I can achieve the same?

Upvotes: 1

Views: 7741

Answers (6)

CertainPerformance
CertainPerformance

Reputation: 370689

Turn the first array into an object indexed by id first, so you can look up the appropriate matching object in O(1) time, and then you can .map the selectedList:

const masterList=[{id:1,name:'Abc'},{id:2,name:'Def'},{id:3,name:'Ghi'}];
const selectedList=[2,3,4];

const masterById = masterList.reduce((a, obj) => {
  a[obj.id] = obj;
  return a;
}, {});

const desiredList = selectedList.map(id => masterById[id]).filter(Boolean);
console.log(desiredList);

Upvotes: 2

Nina Scholz
Nina Scholz

Reputation: 386560

You could take a map with id as key and the object as value and map the wanted values from the map by mapping selectedList.

This approach uses the order from selectedList.

var masterList = [{ id: 1, name: 'Abc' }, { id: 2, name: 'Def' }, { id: 3, name: 'Ghi' }],
    selectedList = [2, 3],
    result = selectedList.map(Map.prototype.get, new Map(masterList.map(o => [o.id, o])));

console.log(result);

Upvotes: 6

Ghoul Ahmed
Ghoul Ahmed

Reputation: 4806

Try this:

let masterList=[{id:1,name:'Abc'},{id:2,name:'Def'},{id:3,name:'Ghi'}];
let selectedList=[2,3];

const result = masterList.filter(({id})=> selectedList.includes(id));

console.log(result);

Upvotes: 2

Cuong Le Ngoc
Cuong Le Ngoc

Reputation: 11975

You can use Array filter() to do this.

Demo:

let masterList=[{id:1,name:'Abc'},{id:2,name:'Def'},{id:3,name:'Ghi'}];
let selectedList=[2,3];

let desiredList = masterList.filter((val) => selectedList.includes(val.id));
console.log(desiredList)

Upvotes: 4

Maheer Ali
Maheer Ali

Reputation: 36564

You can first convert selectedList to Set and then use filter() method array of objects.

You can use Set.prototype.has to check whether the id of the objects exists in the set or not. And this method has O(1) time-complexity. So the time-complexity of the whole algorithm will be linear. 

let masterList=[{id:1,name:'Abc'},{id:2,name:'Def'},{id:3,name:'Ghi'}];
let selectedList = [2,3];
let set = new Set(selectedList);

let res = masterList.filter(x => set.has(x.id));
console.log(res)

Upvotes: 3

Davin Tryon
Davin Tryon

Reputation: 67296

It should be a simple filter on the masterList:

masterList.filter(item => selectedList.includes(item.id));

Upvotes: 4

Related Questions