Javascript - Sum two arrays in single iteration

Question

I want to sum each value of an array of numbers with its corresponding value in a different array of numbers, and I want to do this without looping through each individual value.

So:

var array1 = [1,2,3,4]; var array2 = [5,6,7,8];  var sum    = [6,8,10,12]; 

I'd love to do it in one fell swoop, instead of doing this:

for(var i = 0; i < array1.length; i++){    sum.push(array1[i] + array2[i]); } 

Can anyone think of a way? I'm pretty stumped.

Answer 1

I know this is an old question but I was just discussing this with someone and we came up with another solution. You still need a loop but you can accomplish this with the Array.prototype.map().

var array1 = [1,2,3,4]; var array2 = [5,6,7,8];  var sum = array1.map(function (num, idx) {   return num + array2[idx]; }); // [6,8,10,12] 

Answer 2

Here is a generic solution for N arrays of possibly different lengths.

It uses Array.prototype.reduce(), Array.prototype.map(), Math.max() and Array.from():

function sumArrays(...arrays) {    const n = arrays.reduce((max, xs) => Math.max(max, xs.length), 0);    const result = Array.from({ length: n });    return result.map((_, i) => arrays.map(xs => xs[i] || 0).reduce((sum, x) => sum + x, 0));  }    console.log(...sumArrays([0, 1, 2], [1, 2, 3, 4], [1, 2])); // 2 5 5 4