Array removing, "undefined" and JavaScript

Question

first sorry my english. Im making a little program to sort football players into two teams, A and B. 6 players, 3 for A and 3 for B. With a random number generator of course.

In Java i have no problem, i made this program and runs perfect, but i dont know much about JS and array item removings seems a little diferent here.

My code:

function hola(){
    var primero = document.getElementById("1").value;
    var segundo = document.getElementById("2").value;
    var tercero = document.getElementById("3").value;
    var cuarto = document.getElementById("4").value;
    var quinto = document.getElementById("5").value;
    var sexto = document.getElementById("6").value;

    var jugadores = [primero,segundo,tercero,cuarto,quinto,sexto];
    var eq1=[];
    var eq2=[];

    while (jugadores.length > 0){
        var largoArray = jugadores.length;
        var rand = Math.round(Math.random()* largoArray);
        console.log("before the if, array jugadores haves  ",jugadores.toString() ," and his size is  ",jugadores.length);
        if (eq1.length < 3){
            eq1.push(jugadores[rand]);
            remove(jugadores,jugadores[rand]);
        }else {
            eq2.push(jugadores[rand]);
            remove(jugadores,jugadores[rand]);
        }
    }
    document.getElementById("resultado").innerHTML= eq1 + " y el equipo B: " + eq2;
    console.log("equipo 1 ", eq1);
    console.log("equipo 2", eq2);           
}

function remove(array, element) {
    const index = array.indexOf(element);
    if (index !== -1) {
        array.splice(index, 1);
    }
}

and it return to me:

"equipo 1 (3) [undefined, "iniesta", "ronaldo"] script2.js:35 equipo 2 (4) ["messi", "ronaldinho", "maradona", "pele"]"

also the console logs i made to depurate seems to work fine... The array is 1 element shorter each cicle, and array.lenght match the desired sizes.

What am doing wrong?

CRice · Accepted Answer · 2018-06-08 21:44:58Z

1

The problem is on the line:

Math.round(Math.random() * largoArray)

Since that will sometimes return an index that is beyond the bounds of the array. When that happens, this code:

eq1.push(jugadores[rand]);
remove(jugadores,jugadores[rand]);

Won't work, since jugadores[rand] is undefined, so you end up pushing undefined into one of your arrays, without removing anything from the original jugadores array.

To fix this, use the Math.floor function instead, changing the line to:

Math.floor(Math.random() * largoArray)

answered Jun 8, 2018 at 21:44

CRice

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Comments

dpm · Accepted Answer · 2018-06-08 21:46:44Z

0

Arrays (like Java) start with the index 0.

The range of random numbers you are generating varies from 0 to 6 (array has only 6 elements).

var rand = Math.round(Math.random()* largoArray);

Instead use,

var rand = Math.round((Math.random()* largoArray)-1);

answered Jun 8, 2018 at 21:46

dpm

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1 Comment

Grant Gryczan Over a year ago

No, this can return a negative number. Just use Math.floor and take off the subtraction.

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