compare and merge array in javascript

Question

const arr1 = [{id:1, checked:false},{id:2, checked:false},{id:3, checked:false}]

const arr2 = [{id:1},{id:3}]

i have 2 arrays like above. i want to result should be

arr1 = [{id:1, checked:true},{id:2, checked:false},{id:3, checked:true}]

i tried with array filter, but it gives joined array

companyArr.forEach(citem => {
        mapItem.forEach(mitem => {
            companyArr.push({
            Id: citem.Id,
            CompanyName: citem.CompanyName,
            isChecked: (mitem.company_id === citem.Id)
          })
        })
      })

Nick Parsons · Accepted Answer · 2020-03-14 07:54:57Z

You could make a Set which keeps all your ids from each object in arr2, and then use .map() on arr1 to check the checked values based on whether the set has the current objects id:

const arr1 = [{id:1, checked:false},{id:2, checked:false},{id:3, checked:false}]
const arr2 = [{id:1},{id:3}];

const lut = new Set(arr2.map(({id}) => id));
const res = arr1.map(o => ({...o, checked: lut.has(o.id)}))
console.log(res);

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

Note: I've created a set here for efficient lookup, however, you could use .some() on arr2 if you wish in the .map() as well, but this would have performance drawbacks for large data sets:

const arr1 = [{id:1, checked:false},{id:2, checked:false},{id:3, checked:false}]
const arr2 = [{id:1},{id:3}];

const res = arr1.map(o => ({...o, checked: arr2.some(({id}) => id === o.id)}));
console.log(res);

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

prasanth · Accepted Answer · 2020-03-14 07:04:07Z

1

you could use Array#map for recreate the array .And Array#findIndex for find the first array value exist on 2nd array .And use Spread operator for easy to split the object

const arr1 = [{id:1, checked:false},{id:2, checked:false},{id:3, checked:false}]
const arr2 = [{id:1},{id:3}]

let res =  arr1.map(a=> ({...a,checked: arr2.findIndex(({id}) => id == a.id) > -1}));
console.log(res)

edited Mar 14, 2020 at 7:04

answered Mar 14, 2020 at 6:56

prasanth

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Comments

Ramesh Reddy · Accepted Answer · 2020-03-14 07:06:31Z

1

You can use map and find for that.

const arr1 = [{ id: 1, checked: false }, { id: 2, checked: false }, { id: 3, checked: false }]
  , arr2 = [{ id: 1 }, { id: 3 }]
  , result = arr1.map(el => ({ ...el, checked: !!arr2.find(({ id }) => id === el.id) }));

console.log(result);

edited Mar 14, 2020 at 7:06

answered Mar 14, 2020 at 6:58

Ramesh Reddy

10.7k3 gold badges22 silver badges38 bronze badges

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