how to find difference between two array using lodash/underscore in nodejs

Question

I have two arrays of arrays and am trying to find the difference.

var a = [[ 11, 24, 28, 38, 42, 44 ],
  [ 7, 19, 21, 22, 29, 38 ],
  [ 2, 21, 27, 30, 33, 40 ],
  [ 6, 11, 12, 21, 34, 48 ],
  [ 1, 10, 17, 31, 35, 40 ],
  [ 1, 18, 26, 33, 36, 45 ],
  [ 15, 21, 22, 24, 38, 46 ],
  [ 5, 17, 21, 27, 29, 41 ],
  [ 3, 7, 12, 16, 20, 28 ],
  [ 9, 12, 13, 18, 30, 37 ],
  [ 3, 19, 21, 31, 33, 46 ],
  [ 6, 11, 16, 18, 20, 34 ],
  [ 1, 3, 11, 13, 24, 28 ],
  [ 12, 13, 16, 40, 42, 46 ],
  [ 1, 3, 5, 36, 37, 41 ],
  [ 14, 15, 23, 24, 26, 31 ],
  [ 7, 13, 14, 15, 27, 28 ]];

var b = [[ 4, 7, 9, 21, 31, 36 ],
  [ 2, 5, 6, 12, 15, 21 ],
  [ 4, 7, 8, 15, 38, 41 ],
  [ 11, 24, 28, 38, 42, 44 ],
  [ 7, 19, 21, 22, 29, 38 ]];

How would I find:

c = [[ 2, 21, 27, 30, 33, 40 ],
  [ 6, 11, 12, 21, 34, 48 ],
  [ 1, 10, 17, 31, 35, 40 ],
  [ 1, 18, 26, 33, 36, 45 ],
  [ 15, 21, 22, 24, 38, 46 ],
  [ 5, 17, 21, 27, 29, 41 ],
  [ 3, 7, 12, 16, 20, 28 ],
  [ 9, 12, 13, 18, 30, 37 ],
  [ 3, 19, 21, 31, 33, 46 ],
  [ 6, 11, 16, 18, 20, 34 ],
  [ 1, 3, 11, 13, 24, 28 ],
  [ 12, 13, 16, 40, 42, 46 ],
  [ 1, 3, 5, 36, 37, 41 ],
  [ 14, 15, 23, 24, 26, 31 ],
  [ 7, 13, 14, 15, 27, 28 ]];

I had tried underscore:

_ = require('underscore');
_.difference(a,b);

But it doesn't work.

I also tried lodash:

_ = require('lodash');
_.differenceBy(a,b);

but it doesn't work either.

What am I doing wrong here?

have you installed underscore/lodash properly? have you checked that they were loaded? — Roysh
– Roysh, Commented Aug 10, 2016 at 6:39

alexandre-rousseau · Accepted Answer · 2021-02-24 14:19:03Z

75

Use _.differenceWith, and pass a comparator which compares two arrays, as in:

_.differenceWith(a, b, _.isEqual);

edited Feb 24, 2021 at 14:19

alexandre-rousseau

3,0451 gold badge33 silver badges35 bronze badges

answered Aug 10, 2016 at 6:43

user663031

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7 Comments

steezeburger Over a year ago

I'd like to note that the order of args does matter for _.differenceBy and _.difference. In the documentation for _.differenceBy (lodash), it states: "The order and references of result values are determined by the first array." After some tests I realized the resultant array did not have values from the 2nd array if the 2nd array was longer. The example for _.difference in the documentation seems like a poor choice, being _.difference([2, 1], [2, 3]); // returns [1]. This has me wondering how you'd get [1, 3] if your arrays are eq length, which is what I need.

dsl101 Over a year ago

I had the same problem. In that case (for single-level arrays, so avoiding the With variants), you can do it by _.difference(_.union(a, b), _.intersection(a, b))

dsl101 Over a year ago

And I also just discovered _.xor(), which I think is much neater :). lodash.com/docs/4.17.4#xor

Max Over a year ago

@StanislavMayorov I just tried using _.xor() in the REPL, and it works on arrays with different lengths.

Stanislav Mayorov Over a year ago

@Max yes, it really works. what a surprise. I will delete my comment)

|

KFunk · Accepted Answer · 2018-10-17 07:02:24Z

60

As mentioned by @dsl101,

_.xor([1, 2, 3], [2, 3, 4]);
// [1, 4]

answered Oct 17, 2018 at 7:02

KFunk

3,21226 silver badges36 bronze badges

Comments

Cody Gray · Accepted Answer · 2023-02-28 06:17:00Z

0

If you don't want to use Lodash _.differenceWith, use this naive approach:

function difference(arr1,arr2) {
    let uniqueObj = {}
    let output = []
    for (let i = 0; i < arr1.length; i++) {
        uniqueObj[arr1[i].toString()] = 1
    }
    for (let i = 0; i < arr2.length; i++) {
        uniqueObj[arr2[i].toString()] = 1
    }
    for (let i in uniqueObj) {
        output.push(i.split(',').map(Number))
    }
    return output
}

edited Feb 28, 2023 at 6:17

Cody Gray♦

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answered Feb 28, 2023 at 6:14

leviathan

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