How to subtract one array from another, element-wise, in javascript

Question

If i have an array A = [1, 4, 3, 2] and B = [0, 2, 1, 2] I want to return a new array (A - B) with values [1, 2, 2, 0]. What is the most efficient approach to do this in javascript?

Possible duplicate of [What is the fastest or most elegant way to compute a set difference using Javascript arrays?](https://stackoverflow.com/questions/1723168/what-is-the-fastest-or-most-elegant-way-to-compute-a-set-difference-using-javasc) — jhpratt, Jul 27 '17 at 05:37
A user with your rep should know the importance of sharing effort in question. SO is to get help for your problems and not solution for your requirements — Rajesh, Jul 27 '17 at 05:55
Try this., https://stackoverflow.com/questions/1187518/javascript-array-difference — Anand, Jul 27 '17 at 06:21
Try this link: https://stackoverflow.com/questions/1187518/javascript-array-difference — Anand, Jul 27 '17 at 06:23
The caluclated values in the example are wrong. It should be [1,2,2,0] and not [0,2,2,0]. — Adrian Dymorz, Feb 21 '20 at 19:29

score 122 · Answer 1 · edited Feb 27 '23 at 09:49

122

If you want to find the set difference between two sets, that is, you want all the elements of A that are not in B:

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

If you want arithmetic differences between the elements of A and the corresponding elements of B, then please look to the other posted answers.

edited Feb 27 '23 at 09:49

TMBailey

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answered Oct 31 '18 at 22:17

Andrii Gordiichuk

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explanations would be helpful! – platinums May 08 '19 at 11:18
7

@platinums the solution just filters the array A and returns an array containing all the elements from the array A that are not included in B, effectively subtracting B from A. – John Jul 22 '19 at 12:26
81

This is NOT what rrbest is asking for. – Melroy van den Berg Sep 26 '19 at 21:24
1

@danger89, agree with you, as a simple solution for this (*in case both arrays have the same length*): `ArrA.map((n, i) => n - ArrB[i]);` – Andrii Gordiichuk Oct 08 '19 at 21:49
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By searching for "subtract array" I actually was looking for this answer, lol. Thanks – Sergiy Ostrovsky Jun 17 '20 at 09:49

brk · Answer 2 · 2017-07-27T05:44:54.183

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Use map method The map method takes three parameters in it's callback function like below

currentValue, index, array

var a = [1, 4, 3, 2],
  b = [0, 2, 1, 2]

var x = a.map(function(item, index) {
  // In this case item correspond to currentValue of array a, 
  // using index to get value from array b
  return item - b[index];
})
console.log(x);

edited Jul 27 '17 at 05:44

answered Jul 27 '17 at 05:38

brk

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es6 version: var x = a.map((item, index) => item - b[index]) – Winters Sep 23 '21 at 12:10

Sankar · Answer 3 · 2017-07-27T06:17:52.240

8

For Simple and efficient ever.

Check here : JsPref - For Vs Map Vs forEach

var a = [1, 4, 3, 2],
  b = [0, 2, 1, 2],
  x = [];

for(var i = 0;i<=b.length-1;i++)
  x.push(a[i] - b[i]);
  
console.log(x);

edited Jul 27 '17 at 06:17

answered Jul 27 '17 at 06:11

Sankar

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Both arrays length, suppose to be same. otherwise it can create a problem. Or handle it before. – Avnesh Shakya Jul 27 '17 at 06:19
@AvneshShakya Yes. Both array should be same and that's what asked. – Sankar Jul 27 '17 at 06:26
Strange, for me the JsPerf above doesn't show the for loop as fastest. So I made my own: https://jsperf.com/for-loop-vs-map-vs-for-each-kce and found that for large n the for loop is many times faster. – KCE Jun 16 '18 at 09:14

score 2 · Answer 4 · answered Oct 30 '21 at 06:10

2

One-liner using ES6 for the array's of equal size in length:

 let subResult = a.map((v, i) => v - b[i]); // [1, 2, 2, 0]

v = value, i = index

answered Oct 30 '21 at 06:10

SridharKritha

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score 2 · Answer 5 · edited Dec 23 '21 at 15:20

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const A = [1, 4, 3, 2]
const B = [0, 2, 1, 2]
const C = A.map((valueA, indexInA) => valueA - B[indexInA])
console.log(C) // [1, 2, 2, 0]

Here the map is returning the substraction operation for each number of the first array.

Note: this will not work if the arrays have different lengths

edited Dec 23 '21 at 15:20

TOPKAT

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answered Dec 23 '21 at 09:20

h13o

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As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Dec 23 '21 at 09:35

score 1 · Answer 6 · answered Jul 27 '17 at 06:12

If you want to override values in the first table you can simply use forEach method for arrays forEach. ForEach method takes the same parameter as map method (element, index, array). It's similar with the previous answer with map keyword but here we are not returning the value but assign value by own.

var a = [1, 4, 3, 2],
  b = [0, 2, 1, 2]
  
a.forEach(function(item, index, arr) {
  // item - current value in the loop
  // index - index for this value in the array
  // arr - reference to analyzed array  
  arr[index] = item - b[index];
})

//in this case we override values in first array
console.log(a);

Peter Akinlolu · Answer 7 · 2022-10-01T16:00:05.103

function subtract(operand1 = [], operand2 = []) {
console.log('array1', operand1, 'array2', operand2);
const obj1 = {};

if (operand1.length === operand2.length) {
    return operand1.map(($op, i) => {
        return $op - operand2[i];
    })
}
throw new Error('collections are of different lengths');
}

// Test by generating a random array
function getRandomArray(total){
const pool = []
for (let i = 0; i < total; i++) {
    pool.push(Math.floor(Math.random() * total));
}

return pool;
}
console.log(subtract(getRandomArray(10), getRandomArray(10)))

Time Complexity is O(n) You can also compare your answer with a big collection of arrays.

How to subtract one array from another, element-wise, in javascript

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