CODEWITHSUNDEEP
javascript
rrbest
rrbest

Reputation: 1789

How to subtract one array of numbers from another, element-wise, in JavaScript

If I have an array A = [1, 4, 3, 2] and B = [0, 2, 1, 2], and 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?

Upvotes: 79

Views: 153162

Answers (7)

Andrii Gordiichuk
Andrii Gordiichuk

Reputation: 1939

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.

Upvotes: 136

Peter Akinlolu
Peter Akinlolu

Reputation: 33

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.

Upvotes: 0

h13o
h13o

Reputation: 76

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

Upvotes: 3

SridharKritha
SridharKritha

Reputation: 9671

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

Upvotes: 2

Sankar
Sankar

Reputation: 7107

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);

Upvotes: 8

Kamil Mikosz
Kamil Mikosz

Reputation: 11

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);

Upvotes: 1

brk
brk

Reputation: 50326

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);

Upvotes: 48

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