# Please explain Return Largest Numbers in Arrays

Tell us what’s happening:
Hello, why would this code function when called with [[17, 23, 25, 12], [25, 7, 34, 48], [4, -10, 18, 21], [-72, -3, -17, -10]] return 25,48,21,0 which cannot be found anywhere instead of 25, 7, 34, 48 which is a close match ?

``````
function largestOfFour(arr) {
// You can do this!
var result = [];
for (let i=0; i < arr.length; i++) {
var largest = 0;
for (var ir=0; ir < arr[i].length; ir++) {
if (arr[i][ir] > largest) {
largest = arr[i][ir];
}
}
result[i] = largest;
}
return result;
}

console.log(largestOfFour([[17, 23, 25, 12], [25, 7, 34, 48], [4, -10, 18, 21], [-72, -3, -17, -10]]));
``````

User Agent is: `Mozilla/5.0 (Windows NT 6.2; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.131 Safari/537.36`.

I think you haven’t quite got the instructions. The function doesn’t return the ‘largest’ array of the four supplied, it returns the largest number in each of those arrays - as an array.

So, in array 1, it finds 25, in array 2 it finds 48, etc. These four largest numbers are returned as an array. In array 4 (the one with all the negatives) it returns 0 because you declared `largest` to be zero and none of the array items were greater than (`>`) it

From the challenge:

Return an array consisting of the largest number from each provided sub-array.

From the sub-array `[17, 23, 25, 12]`, which number contained within is the largest?
Now, from the sub-array `[25, 7, 34, 48]`, which number contained within is the largest?

Apply this line of questioning to all the sub-arrays and you should get

• 25
• 48
• 21
• -3

From the last result, we can see that the largest number could have a negative value.
The following bit of code shows why you’re getting 0 instead of -3 for your last value.

``````  var largest = 0;
for (var ir=0; ir < arr[i].length; ir++) {
if (arr[i][ir] > largest) {
largest = arr[i][ir];
}
}
result[i] = largest;
``````

You should look into using the `.map()` method here.