Javascript arrays of Objects; Subtract one from another

Question

Put simply, I want to subtract one array from another.

The arrays are arrays of objects. I understand I can cycle through one array and on each item, comparing values in the other array, but that just seems a little messy.

Thanks for the help, hopefully this question isnt too basic, I have tried googling it with no luck :(

EDIT:

The Objects in the Arrays I wish to remove will have identical values but are NOT the same object (thanks @patrick dw). I am looking to completely remove the subset from the initial array.

Do the arrays hold references to the *same* objects, or are they references to unique objects with potentially the same data? `{a:1} != {a:1}` yet `var a = b = {a:1}; a == b` — user113716, Jan 06 '11 at 22:59
I'm not quite sure this question is specific enough. In what way do you want to subtract these arrays? Are you looking to subtract them such that the nth element of the new array is the nth element of the first minus the nth element of the second? Or is your intent rather to do some sort of "set difference" on these arrays? — avpx, Jan 06 '11 at 23:02
thanks for the comments. I have edited the question to better explain the problem. — neolaser, Jan 07 '11 at 00:43

Adrian Dymorz · Answer 1 · 2020-02-21T19:51:46.497

This answer is copied from https://stackoverflow.com/a/53092728/7173655, extended with a comment and a solution with objects.

The code filters array A. All values included in B are removed from A.

const A = [1, 4, 3, 2]
const B = [0, 2, 1, 2]
console.log(A.filter(n => !B.includes(n)))

The same with objects:

const A = [{id:1}, {id:4}, {id:3}, {id:2}]
const B = [{id:0}, {id:2}, {id:1}, {id:2}]
console.log(A.filter(a => !B.map(b=>b.id).includes(a.id)))

score 3 · Accepted Answer · answered Jan 06 '11 at 23:04

3

http://phpjs.org/functions/index

There is no built-in method to do this in JavaScript. If you look at this site there are a lot of functions for arrays with similar syntax to PHP.

answered Jan 06 '11 at 23:04

sissonb

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link not found. – Dennis Hackethal Jan 05 '22 at 23:00
@weltschmerz here's a copy from the wayback machine https://web.archive.org/web/20130713181607/http://phpjs.org/functions/ – sissonb Jan 06 '22 at 03:17

score 2 · Answer 3 · answered Jan 06 '11 at 23:00

2

http://www.jslab.dk/library/Array

This site has some js functions on "sets"

I think you need the diff function.

answered Jan 06 '11 at 23:00

Marnix

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score 1 · Answer 4 · answered Jan 05 '22 at 22:57

It should remove all values from list a, which are present in list b keeping their order.

  let a = [0, 2, 5, 6, 1];
  let b = [2, 6, 2, 5, 0];

  function arrayDiff() {
    for (i of b) {
      for (j of a) {
        if (i === j) {
          a.splice(a.indexOf(j), 1);
        }
      }
    }
    return a;
  }

Javascript arrays of Objects; Subtract one from another

4 Answers4