Loop Through Nested Array Elements With JavaScript

Question

I'm trying to loop through nested arrays to determine if an element in the array is either "open" or "senior":

function openOrSenior(data) {

  for (let i = 0; i <= data.length; i++) {

    let dataElement = data[i];

    for (let j = 0; j <= dataElement.length; j++) {

      if (dataElement[0] >= 55 && dataElement[1] > 7) {

        return ["Senior"];

      }

      return ["Open"];

    }
  }
}

Given the input of

[[18, 20],[45, 2],[61, 12],[37, 6],[21, 21],[78, 9]]

The function should output

["Open", "Open", "Senior", "Open", "Open", "Senior"]

But currently it looks like it's only looping through the first element in the main array ([18, 20]) because my function is only returning:

["Open"]

Why is this function failing to continue to loop through the other nested arrays and return either "Open" or "Senior"? Possibly a problem with the scope?

https://www.codewars.com/kata/categorize-new-member/train/javascript

I was trying to implement what I found here, which suggested a for-loop within a for-loop.

Why do you need the second loop? There are only two elements in `dataElement` and you are mentioning them by index, so why the second loop? — Ed de Almeida, Mar 28 '19 at 20:14
Oh yes, true - removing the second for-loop still returns, `[Open]`, though. — HappyHands31, Mar 28 '19 at 20:17

score 2 · Accepted Answer · answered Mar 28 '19 at 20:16

You are returning whenever the check succeeds or not, and you've got a redundant for loop. You should iterate the array with a single for loop, and according to the check push Senior or Open to the result array. In the end return the result array.

function openOrSenior(data) {
  const result = [];

  for (let i = 0; i < data.length; i++) {
    const dataElement = data[i];

    if (dataElement[0] >= 55 && dataElement[1] > 7) {
      result.push("Senior");
    } else result.push("Open");
  }

  return result;
}

console.log(openOrSenior([[18, 20],[45, 2],[61, 12],[37, 6],[21, 21],[78, 9]]));

Or you can use Array.map():

const openOrSenior = data => 
  data.map(([a, b]) => 
    a >= 55 && b > 7 ? 'Senior' : 'Open'
  )

console.log(openOrSenior([[18, 20],[45, 2],[61, 12],[37, 6],[21, 21],[78, 9]]))

score 2 · Answer 2 · answered Mar 28 '19 at 20:19

You need only a single loop and an array for the values.

function openOrSenior(data) {
    var result = [];
    for (let i = 0; i < data.length; i++) {
        let [left, right] = data[i];
        result.push(left >= 55 && right > 7
            ? "Senior"
            : "Open"
        );
    }
    return result;
}

console.log(openOrSenior([[18, 20], [45, 2], [61, 12], [37, 6], [21, 21], [78, 9]]));

Loop Through Nested Array Elements With JavaScript

2 Answers2