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Hello StackOverflowCommunity! My name is Piet.

While investigating the beloved Javascript I got a bit stuck:

I´m not sure why I get 98 empty items pushed into my Array.

On Index[0] and Index[99] I get IntegerValues as expected.

Thank you for your answers! :)

// create an Array with the size of N(x) and 
// fill it with numbers in a range from 0 to 100 randomly.

createNSizedArray = (x) => {

    for(let i = 0; i < x; i++) {
        var arr = [];
        arr[i] = arr.push(Math.round(Math.random()*100));
        
    }
    return arr;
}

console.log(createNSizedArray(100)); 

// output -> [ 31, <98 empty items>, 1 ];

// Why are the other 98 items in the Array empty and how to change them into integer values?

Actually I inspected the Items[1-98] to find out their values and to check if they are really empty.

But:

console.log(arr[4]) for example return "undefined" to me. So they are not really empty.

PietOverloop
  • 1

5 Answers5

1

You are getting a mostly undefined array because you are defining a new variable arr at each iteration. You should move the declaration of arr outside of the loop.

Here is a quick alternative: Array(100).fill().map(_=>Math.round(Math.random()*100))

Vincent
  • 453
  • 3
  • 6
1

Try moving the initialization of the array before the for loop. This makes sure that you don't make a new array every time the loop runs.

Sam
  • 11
  • 1
0

It is because you are creating a new array on each iteration. Try this:

createNSizedArray = (x) => {
  var arr = [];
  for (let i = 0; i < x; i++) {
    arr[i] = arr.push(Math.round(Math.random() * 100));
  }
  return arr;
};
Krystian Sitek
  • 573
  • 3
  • 7
0

Possible solution:

const createNSizedArray = (x) => {
    // it had to be moved outside the for-loop to prevent from setting everything so far to an empty array
    let arr = [];
    for (let i = 0; i < x; i++) {
        // here you don't need both arr.push(...) and assignment
        arr[i] = Math.round(Math.random()*100);
        
    }
    return arr;
}

console.log(createNSizedArray(100));

What Array.prototype.push does:

let arr = [];
console.log(arr);

arr.push(1);
console.log(arr); // [1]

arr.push(2);
console.log(arr); // [1,2]

arr.push(3);
console.log(arr); // [1,2,3]

What you're trying to achieve, as @Vincent suggested, can easily be done with:

Array(100).fill().map(_ => Math.round(Math.random() * 100))
orustammanapov
  • 1,792
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  • 44
0

you could use the Array method.

    const createNSizeArray = (n) => {
          return Array.from({ length: n }, () => Math.round(Math.random()*100 );
        };
        
    console.log(createNSizeArray(5)) // [81, 92, 23, 54, 12]
Chadjaa Sofianne
  • 67
  • 3