Generate unique numbers

Question

I'm trying to make array of seven random numbers so far this is my code:

function lotoGenerator() {
        var array = [];
        var i;
    for (i = 0; i <=6; i++) {
        var temp = Math.floor((Math.random() * 39) + 1);
        array.push(temp);
    }    
    console.log(array);
}
lotoGenerator();

Now with this code I can get results like this [30, 6, 36, 8, 16, 27, 6]. As you can see number 6 come out two times. Is there a way to make array not repeat numbers. I'm new to javaScript and I wasn't able to implement solutions I found online.

Do you want to always get 7 distinct numbers? – mm759 Nov 22 '16 at 17:55 — mm759, Nov 22 '16 at 17:55

Elias Soares · Accepted Answer · 2016-11-22T18:09:39.527

7

Place a do ... while statement on your random generation that check if the number was already on the loto numbers.

function lotoGenerator() {
        var array = [];
        var i;
    for (i = 0; i <=6; i++) {
        do {
            // Generate your random number
            var temp = Math.floor((Math.random() * 39) + 1);
            // If the number already exists, the index of it on loto array will be different of -1, so it already exists
            var alreadyExists = array.indexOf(temp) !== -1;
        } while (alreadyExists) // Repeat this many times necessary to get an unique number.

        array.push(temp);
    }    
    console.log(array);
}
lotoGenerator();

Note that this isn't the most efficient solution since you can have the bad luck of having the same number sorted many times, so the do...while loop may run too many times.

The best way to solve this is by having an array with available numbers and removing the drawn number:

function lotoGenerator() {
    var available = [];
    var drawn = [];
    for (var i = 1; i<= 40; i++) {
        available.push(i);
    }

    for (i = 0; i <=6; i++) {
        var random = Math.floor((Math.random() * available.length));
        drawn.push(available[random]);
        available.splice(random, 1);
    }

    return drawn;
}

This second function have an well known execution time, and will be more efficient as the number of random elements increase.

edited Nov 22 '16 at 18:09

answered Nov 22 '16 at 17:55

Elias Soares

9,884
4
29
59

can i use goto statement here ?? – Mahi Nov 22 '16 at 18:01
@mahi Javascript do not implement goto statement, also a `do..while` block is easy to understand. – Elias Soares Nov 22 '16 at 18:11
Thank you for your answer. Can you explain "var alreadyExists = array.indexOf(temp) !== -1; " in more detail. I'm trying to grasp the concept but i'm having trouble. – Karadjordje Nov 22 '16 at 18:19
@Karadjordje it will find the index of element from array . if it don't fin it will return `-1` – Mahi Nov 22 '16 at 18:20
One more question in your second solution. Why did you use "available.splice(random, 1);" ??? – Karadjordje Nov 22 '16 at 18:55
Array splice removes the element from the available array. It avoids that the number was choiced twice. – Elias Soares Nov 22 '16 at 21:12

score 3 · Answer 2 · answered Nov 22 '16 at 17:57

This is one of the options:

function lotoGenerator() {
    var array = [], i = 0, temp;
    while (i <= 6) {
        temp = Math.floor((Math.random() * 39) + 1);
        if ( array.indexOf(temp) > -1 ) continue;
        i = array.push(temp);
    }    
    console.log(array);
}

Mr.7 · Answer 3 · 2016-11-22T18:24:27.040

1

Adding if(array.indexOf(temp) > -1) continue; will do the trick to your code.

function lotoGenerator() {
        var array = [];
    while (array.length <= 6) {
        var temp = Math.floor((Math.random() * 39) + 1);
        if(array.indexOf(temp) > -1) continue;
        array.push(temp);
    }    
    console.log(array);
}
lotoGenerator();

edited Nov 22 '16 at 18:24

answered Nov 22 '16 at 17:59

Mr.7

2,292
1
20
33

Generate unique numbers

3 Answers3