Filter object with keys in array

Question

I have this array

const array = [1, 3, 6];

and this object

const obj = {
   1: {id: 1, foo: 'a', ...},
   2: {id: 2, foo: 'b', ...}
   3: {id: 3, foo: 'c', ...},
   4: {id: 4, foo: 'd', ...},
   5: {...},
   6: {...}
   ... // up to 1000 key/value paris
};

I wonder how to filter the obj with the keys in the array. One way would be

obj.filter(elem => elem.id...);

But that iterates through all the elements in the obj, eventhough there are just three elements in the array. Better would be to iterate over the array, but

array.filter(elem => elem === obj.id ...);

then only returns the elements from the array(meaning, 1, 3, 6). What I need is an array looking like

const result  = ['s', 'b', 'c', 'd'];

What is the best way to do this?

I mean what are these values foo and bar? Additionally, will there be any values in the array that does not exist in the obj? — Nikhil Aggarwal
– Nikhil Aggarwal, Commented Jun 14, 2019 at 6:57

Shubham Khatri · Accepted Answer · 2019-06-14 07:18:15Z

6

You can map over the array and and return the key foo from within the object

const res = array.map(elem => obj[elem].foo);

If all elements don't exists in the object you can add a filter condition to remove undefined values

const res = array.map(elem => obj[elem] &&obj[elem].foo).filter(Boolean);

edited Jun 14, 2019 at 7:18

answered Jun 14, 2019 at 6:55

Shubham Khatri

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2 Comments

georg Over a year ago

Provided all array elements actually exist in obj.

Shubham Khatri Over a year ago

@georg, yes you are right. I updated the answer to take care of the undefined case too

Nina Scholz · Accepted Answer · 2019-06-14 08:38:43Z

4

If you have the id as key, you could map the wanted values by filtering the keys for getting only known key and then map the value.

const
    array = [1, 3, 6],
    object = { 1: { id: 1, foo: 'bar' }, 2: {}, 3: { id: 3, foo: 'foo' }, 4: {}, 5: {} },
    result = array 
        .filter(Object.hasOwnProperty.bind(object))
        .map(id => object[id].foo);

console.log(result);

edited Jun 14, 2019 at 8:38

answered Jun 14, 2019 at 6:55

Nina Scholz

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Nikhil Aggarwal · Accepted Answer · 2019-06-14 07:07:08Z

1

If all the values in array exist in obj then use Array.map else if there are missing entries in obj then can use Array.reduce

const array = [1, 3, 6];
const obj = {1: {id: 1, foo: 'bar'},2: {id: 2, foo: 'foo'}};
 
const result = array.reduce((a,c) => obj[c] ? a.concat(obj[c].foo) : a, []);;
console.log(result);

answered Jun 14, 2019 at 7:07

Nikhil Aggarwal

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Comments

Syed Afzal · Accepted Answer · 2019-06-14 07:02:15Z

0

You don't need to iterate all the objects you just need to check whether the key is exist or not, if the key is exists you push the foo value to the result array Here's the code :

const array = [1, 3, 6];

const obj = {
    1: {id: 1, foo: 'bar'},
    2: {id: 2, foo: 'foo'},
    3: {},
    4: {},
    5: {},
    6: {}
};

let result = [];

array.forEach((el) => {
    if(obj.hasOwnProperty(el)){
        result.push(obj[el].foo)
    }
});

console.log(result);

answered Jun 14, 2019 at 7:02

Syed Afzal

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