Function accessing Array of Array

JavaScript
1

Hello, I am new to the forum and early on in my JavaScript learning. I have a problem that has me stumped which is using a function to access an array within an array and then summing the values at the specific index.

Here I am using a for loop to access elements of the array and then adding them and I get the expected result. However I believe this approach would be considered “hard coding” for the array. When I try to build a function, to access the values, it does not work. Any assistance to point me in the right direction would be greatly helpful.

Here is my for loop of the specific array:

const numbers = [
  [-4, 2, 1],
  [0, -1, 2],
  [2, 2, 3]
];
  for (var i = 0; i < numbers.length; i++) {
       for (var j = 0; j < numbers[i].length; j++) {
    var sum = numbers[0][2] + numbers[1][2] + numbers[2][2];
    var sum2 = numbers[0][0] + numbers[1][0] + numbers[2][0];
      }
 }
console.log(sum); //--> returns 6 (i.e. 1 + 2 + 3)
console.log(sum2);//--> returns -2 (i.e. -4 + 0 + 2)

However when I try to perform this same action with a function it is not returning the expected results:

const numbers = [
  [-4, 2, 1],
  [0, -1, 2],
  [2, 2, 3]
];
function addNestedNumbers(arr, identifier) {
  for (var i = 0; i < arr.length; i++) {
     for (var j = 0; j < arr[i].length; j++) {
     
    }
   return arr[identifier];
  }
  //sumTotal = arr[i] + arr[j];
//return sumTotal;
}
// Examples:
console.log(addNestedNumbers(numbers, 2));  //--> returns 6 (i.e. 1 + 2 + 3)
//console.log(addNestedNumbers(numbers, 0));  //--> returns -2 (i.e. -4 + 0 + 2)
2

you don’t need the second loop, you can do it with only one loop, because the inner array has a fixed index to access.
access each array with the i loop, then get the item at index identifier from there, and sum it to your running total

4

Thank you. So I would use a single for loop to iterate over the outer array but then how would I access the fixed index of a given position within the inner array? I’m early in my JavaScript journey so any direction/example you could offer would be greatly appreciated

5

you use bracket notation, you access the outer array with the index of the loop, and then the fixed index

6

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