relative complement of A in B with functional programming

Question

I have to retrieve the values that exist only on Array B, but do not exist on Array A.

From my research, It is called:

relative complement of A in B

Values in the arrays may not be primitives.I need an efficient and functional apporach to this problem. I have found lodash _.without function, but it supports only array of primitive numbers.

Array A:

[{
    id: 1
},
{
    id:2
}]

Array B:

[{
    id:2
},
{
    id:3
}]

result should be:

[{
    id:3
}]

this object is the only one who exist on Array B, but not on Array A.

Your image is even used here: http://www.competa.com/blog/oneliner-set-operations-arrays/ - I found that when googling "relative complement javascript" - just rewrite the filter: `let result = [...new Set(B.filter(item => !A.includes(item)))];` — mplungjan, Jan 15 '18 at 08:36
yes. however, it solves the problem for primitive numbers (loddash function does it too). i am looking for functional approach with a function that can compare. — LiranC, Jan 15 '18 at 08:38

Nina Scholz · Accepted Answer · 2018-01-15T09:02:24.897

You could use a comparison function which takes two objects and check the id for unequalness.

var aa = [{ id: 1 }, { id: 2 }],
    bb = [{ id: 2 }, { id: 3 }],
    comparison = (a, b) => a.id !== b.id,
    result = bb.filter(b => aa.every(a => comparison(a, b)));

console.log(result);

With a check for equalness

var aa = [{ id: 1 }, { id: 2 }],
    bb = [{ id: 2 }, { id: 3 }],
    comparison = (a, b) => a.id === b.id,
    result = bb.filter(b => aa.every(a => !comparison(a, b)));

console.log(result);

score 1 · Answer 2 · answered Jan 15 '18 at 08:37

1

You can use array#filter with array#some. Iterate through arrB and check if the arrA contains that id using array#some and negate the result of array#some.

var arrA = [{id: 1},{id:2}],
    arrB = [{id:2},{id:3}],
    result = arrB.filter(({id}) => !arrA.some(o => o.id === id));
console.log(result);

answered Jan 15 '18 at 08:37

Hassan Imam

21,956
5
41
51

thanks, however the solution is hard-coded, there's a need for functional solution, it should accept a comparison function :) – LiranC Jan 15 '18 at 08:45
You can wrap this a method passing your comparison criteria. – Hassan Imam Jan 15 '18 at 08:59

score 0 · Answer 3 · answered Jan 15 '18 at 08:36

0

You can use array.prototype.filter and array.prototype.findIndex:

var arrayA = [{ id: 1 }, { id: 2 }];
var arrayB = [{ id: 2 }, { id: 3 }];

var result = arrayB.filter(b => arrayA.findIndex(a => a.id === b.id) === -1);
console.log(result);

answered Jan 15 '18 at 08:36

Faly

13,291
2
19
37

score 0 · Answer 4 · answered Mar 26 '21 at 08:30

0

If you want to use lodash, _.differenceBy could be of use:

relativeComplementOfAinB = _.differenceBy(arrayB, arrayA, v => v.id);

answered Mar 26 '21 at 08:30

wensveen

783
10
20

relative complement of A in B with functional programming

4 Answers4