Return Largest Numbers in Arrays: can't reproduce the simplest solution into the loop

JavaScript
#1

Tell us what’s happening:

When I tried this

function largestOfFour(arr) {
  let x, y = []
  
    x = arr.shift()
    console.log(x)// returns 4,5,1,3
    y = Math.max(...x)
    console.log(y)//returns 5

    x = arr.shift()
    console.log(x)// return 13,27,18,26
    y = Math.max(...x)
    console.log(y)//return 27

//etc.

  return arr;
}

largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);

It prints the largest number of one array. But when I put this into a loop. It returns “-Infinity”
Your code so far


function largestOfFour(arr) {
  let x, y = []
  for (let i = 0; i < arr.length; i++){
   x = arr[i].shift()
   y = Math.max(...x)
  }
  console.log(y)
  
  return y;
}

largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);


/**  x = arr.shift()
    console.log(x)
    y = Math.max(...x)
    console.log(y) */

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Link to the challenge:

#2

try looking st what happens in your code using the JavaScript Tutor
look at the value each variable get, is the value you expect?

#3

I was expecting at the first iteration that x = [4, 5, 1, 3]. But it seems that is equal to 4. Due to that the following line doesn’t do anything.

#4

you may want to check what shift does and on what array you used it on

#5

shift takes the 1st element of an array (changing the array). I wanted to applied to each element of the main array intending to then apply Math.max to each of those elements (like if [4, 5, 1, 3] was going to return 5).

#6

Finally, I landed this:

function largestOfFour(arr) {
  let x, y, z = []
  for (let i = 0; i < arr.length; i++){
   x = arr[i]
   y = Math.max(...x)
   z.push(y)     
  }
  return z;
}

largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);```

It did work. I haven’t seen the FCC solution. But I think my main problem was that I didn’t realize how to use methods like push to really store the value required from each iteration.

Am I right?

#7

And, about my solution: would it be Procedural or Declarative? Some source to found out the concept?

#8

Hi @leoncpaulo
I find this solution simpler to understand using for-in loop and Math.max() of a spread array:

        function largestOfFour(arr) {
          // You can do this!
          let r = [];
          for (let a in arr){
                r.push(Math.max(...arr[a]));
          }
          return r;
        }
                
        largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);

I hope it helps.

#9