Ramda: get objects from array by comparing with each item in another array

Question

I've an array like:

ids = [1,3,5];

and another array like:

items: [
{id: 1, name: 'a'}, 
{id: 2, name: 'b'}, 
{id: 3, name: 'c'}, 
{id: 4, name: 'd'}, 
{id: 5, name: 'e'}, 
{id: 6, name: 'f'}
];

What I want is another array like:

array = [{id: 1, name: 'a'}, {id: 3, name: 'c'}, {id: 5, name: 'e'}];

I can't get my head around it. so far i tried like:

console.log(R.filter(R.propEq('id', <donnow what shud be here>), items);
console.log( R.pick(ids)(items))

score 5 · Accepted Answer · edited Sep 12 '19 at 07:10

5

If you still want to do with Ramda:

const ids = [1,3,5];

const items = [
{id: 1, name: 'a'}, 
{id: 2, name: 'b'}, 
{id: 3, name: 'c'}, 
{id: 4, name: 'd'}, 
{id: 5, name: 'e'}, 
{id: 6, name: 'f'}
];

console.log(

  R.filter(R.compose(R.flip(R.contains)(ids), R.prop('id')), items)

);

<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.26.1/ramda.min.js"></script>

edited Sep 12 '19 at 07:10

customcommander

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answered Nov 18 '16 at 15:01

cstuncsik

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score 4 · Answer 2 · answered May 07 '16 at 17:18

4

You can use .filter and .indexOf. Note these are ECMA5 methods for Arrays, and will not work in IE8.

var ids = [1, 3, 5];
var items = [
  {id: 1, name: 'a'}, 
  {id: 2, name: 'b'}, 
  {id: 3, name: 'c'}, 
  {id: 4, name: 'd'}, 
  {id: 5, name: 'e'}, 
  {id: 6, name: 'f'}
];

var filtered = items.filter(function(obj) {
  return ids.indexOf(obj.id) > -1;
});
console.log(filtered); // [{id: 1, name: 'a'}, {id: 3, name: 'c'}, {id: 5, name: 'e'}];

answered May 07 '16 at 17:18

Andreas Louv

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This is correct! You will however need to add a polyfill if you are targeting IE8 and below – Andreas Louv May 07 '16 at 17:23

score 4 · Answer 3 · answered May 07 '16 at 17:55

4

Or may be one liner without Ramda

items.filter(x=>ids.includes(x.id))

answered May 07 '16 at 17:55

Jagdish Idhate

7,513
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score 1 · Answer 4 · answered May 07 '16 at 17:26

1

I suggest to use a hash table for faster lookup.

var ids = [1, 3, 5],
    items = [{id: 1, name: 'a'}, {id: 2, name: 'b'}, {id: 3, name: 'c'}, {id: 4, name: 'd'}, {id: 5, name: 'e'}, {id: 6, name: 'f'} ],
    filtered = items.filter(function(obj) {
        return this[obj.id];
    }, ids.reduce(function (r, a) {
        r[a] = true;
        return r;
    }, Object.create(null)));

document.write('<pre>' + JSON.stringify(filtered, 0, 4) + '</pre>');

answered May 07 '16 at 17:26

Nina Scholz

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This is quite useful when you have a large collection and/or when you want to curry the ids into a reusable function. I probably wouldn't accept the overhead of creating that temporary structure otherwise. – Scott Sauyet Sep 12 '19 at 13:06
Also, while I usually find your code quite easy to read, something about the indentation here seems off. `Object.create...` looks to be a third parameter to `filter`. – Scott Sauyet Sep 12 '19 at 13:09
you are right, the formatting is wrong, but today i wouls write it with a `Set` instead (as variable, not as `thisArg`). – Nina Scholz Sep 12 '19 at 13:12
Yes, I had somehow missed that this was an old post when it came to my attention today. Sorry about that. – Scott Sauyet Sep 12 '19 at 13:29

Ramda: get objects from array by comparing with each item in another array

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