Adding two arrays and returning a new array

Question

Write a function addArrays that takes 2 arrays of numbers as parameters and returns a new array where elements at same index position are added together. For example: addArrays([1,2,3], [4,3,2,1]); // => [5,5,5,1]

I am trying to use nested for loops but its giving an incorrect answers....

  function addArrays(num1, num2){
      var result = [];
      for(var i=0; i< num1.length; i++){
        for(var j=0; j<num2.length; j++){
          result.push(num1[i] + num2[j]);
      }
      }
      return result;
    }

possible duplicate of http://stackoverflow.com/questions/24094466/javascript-sum-two-arrays-in-single-iteration — bob, May 19 '16 at 18:57
No need for nested loops, but you have to check arrays length... — sinisake, May 19 '16 at 19:00

score 4 · Answer 1 · answered May 19 '16 at 19:00

I suggest to use only one loop with a check of the length and some default values if the elements do not exists.

function addArrays(array1, array2) {
    var i,
        l = Math.max(array1.length, array2.length),
        result = [];
    for (i = 0 ; i < l; i++) {
        result.push((array1[i] || 0) + (array2[i] || 0));
    }
    return result;
}

console.log(addArrays([1, 2, 3], [4, 3, 2, 1]));

score 2 · Answer 2 · answered May 19 '16 at 19:00

There is no need to nest with 2 loops. Nested loops for arrays are used if you have a 2 dimensional array.

function addArrays(num1, num2){
    var result = [];
    var size = Math.max(num1.length, num2.length);

    for(var i = 0; i < size; i++){
        result.push(num1[i] + (num2[i]);

    }
    return result;
}

You can also default it to 0 if the arrays are different lengths and you go off the end like this

(num1[i] || 0) + (num2[i] || 0)

This chooses either the number in the array, or 0 if it doesnt exist

score 0 · Answer 3 · answered May 19 '16 at 18:55

0

function addArrays(num1, num2){
      var result = [];
      for(var i=0; i< num1.length; i++){
          result.push(num1[i] + num2[i]);
      }
      return result;
}

answered May 19 '16 at 18:55

chiarotto.alessandro

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mferly · Answer 4 · 2016-05-19T20:51:58.340

0

For those a little more progressive in nature...

let a = [1, 2, 3], b = [4, 3, 2, 1], l = Math.max(a.length, b.length)
const addArrays = ((a[l-1]) ? a : b).map((v, k) => (a[k] || 0) + (b[k] || 0))

console.log(addArrays) // [ 5, 5, 5, 1 ]

edited May 19 '16 at 20:51

answered May 19 '16 at 20:01

mferly

1,646
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1

`Math.max(...a, ...b)` it does not check the length, but the elements. – Nina Scholz May 19 '16 at 20:19

Adding two arrays and returning a new array

4 Answers4