Filter an array of objects and extract its property by using an array of keys

Question

im having this problem which i cant wrap around my head,

much better if put in a code.

//Array of objects sample
var objects = [{id:1, name:'test1'}, {id:2, name:'test2'}, {id:3, name: 'test3'}, {id:4, name:'test4'}];
var arrayOfKeys = [3,1,4];

//extract object name property if its id property is equivalent to one of arrayOfKeys [3,1] 
//var arrayOfKeys = [3,1,4];
//output sample: extractedName=['test3','test1','test4'];

i've been using filter and map but no avail, also tried nesting filter inside map im getting an arrays of array and inside is a single object.

Are the names always going to be testN where N is a number? — ibrahim mahrir
– ibrahim mahrir, Commented Jun 20, 2017 at 16:37
@ibrahimmahrir yes, its continuous, even i add another id to arrayOfKeys it should still correspond to the id property of the object — Romyeo
– Romyeo, Commented Jun 20, 2017 at 16:43

Nina Scholz · Accepted Answer · 2017-06-20 16:38:13Z

2

You could map the objects and ren map the wanted keys for getting the name.

var objects = [{ id: 1, name: 'test1' }, { id: 2, name: 'test2' }, { id: 3, name: 'test3' }],
    arrayOfKeys = [3, 1],
    result = arrayOfKeys.map((map => id => map.get(id).name)(new Map(objects.map(o => [o.id, o]))));
    
console.log(result);

answered Jun 20, 2017 at 16:38

Nina Scholz

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2 Comments

trincot Over a year ago

Nice and concise!

Rick Over a year ago

@Andreas I am going to have to disagree. Her answers always super efficient and I am always learning something new from her code.

Egor Stambakio · Accepted Answer · 2017-06-20 16:43:25Z

0

I assume you need to map array numbers to id properties? Here's the code where you map through numbers and find inside your array to handle situations when there's no such id in objects array:

var objects = [{id:1, name:'test1'}, {id:2, name:'test2'}, {id:3, name: 'test3'}];
var arrayOfKeys = [3,1];

var res = arrayOfKeys.map(key => {
  var found = objects.find(o => o.id == key);
  return found ? found.name : false;
})

console.log(res)

answered Jun 20, 2017 at 16:43

Egor Stambakio

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ibrahim mahrir · Accepted Answer · 2017-06-20 16:48:52Z

0

let objects = [{id:1, name:'test1'}, {id:2, name:'test2'}, {id:3, name: 'test3'}, {id:4, name:'test4'}],
    arrayOfKeys = [3,1,4];

let result = objects.reduce((res, obj) => {    // loop over the array of objects
  let index = arrayOfKeys.indexOf(obj.id);     // check if the current object's id is in the array of keys
  if(index !== -1) {                           // if it's there
    res.push(obj.name);                        // then add the current object's name to the result array
    arrayOfKeys.splice(index, 1);              // remove its id from the array of keys so we won't search for it again (optional, slightly better than leaving it there)
  }
  return res;
}, []);

console.log(result);

answered Jun 20, 2017 at 16:48

ibrahim mahrir

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Comments

Rick · Accepted Answer · 2017-06-20 21:06:33Z

0

I think you were on the right track with the filter. You can make it readable and concise with some.

var objects = [{id: 1,name: 'test1'}, {id: 2,name: 'test2'}, {id: 3,name: 'test3'}, {id: 4,name: 'test4'}],
arrayOfKeys = [3, 1, 4];

var result = objects.filter((x, i) => {
  if (arrayOfKeys.some(k => x.id === k)) {
    return true;
  }
})
console.log(result.map(x=>x.name));

Something even shorter! would be

var objects = [{id: 1,name: 'test1'}, {id: 2,name: 'test2'}, {id: 3,name: 'test3'}, {id: 4,name: 'test4'}],arrayOfKeys = [3, 1, 4];

var result = objects.filter((x, i) => arrayOfKeys.some(k => x.id === k));

console.log(result.map(x=>x.name));

edited Jun 20, 2017 at 21:06

answered Jun 20, 2017 at 21:00

Rick

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