Javascript - Math.random improvements

Question

I'm currently working on a small game that needs to return either 1,2 or 3.

The idea is that I then compare two numbers and the greater wins.

The code i'm using is this:

var isMultipleOf, number1, number2, random;

random = function(number) {
  return isMultipleOf(Math.floor((Math.random() * number) + 1));
};

isMultipleOf = function(number) {
  if (number % 2 === 0) {
    return 1;
  }
  if (number % 3 === 0) {
    return 2;
  } else {
    return 3;
  }
};

number1 = random((Math.random() * 100) + 1);
number2 = random((Math.random() * 100) + 1);

console.log("number 1 is " + number1 + " and number2 is " + number2);

This code works, but i'd like to improve it a bit if possible.

With my game, a draw is possible, but with my current logic it happens quite often and I don't like it. Can you suggest a better way to improve this making it less possible to get a draw (same numbers)?

thanks

I'm voting to close this question as off-topic because it refers to working code, and therefore should be posted to the Code Review SE site. — Joe Clay
– Joe Clay, Commented Aug 3, 2017 at 15:44
There's plenty of questions here on SO asking for better way to do things, i don't see why this would be off-topic to be honest — Nick
– Nick, Commented Aug 3, 2017 at 15:45
The existence of off-topic questions which haven't been closed yet doesn't make another off-topic question on topic. — Quentin
– Quentin, Commented Aug 3, 2017 at 15:48
isMultipleOf doesn't return 1, 2 or 3 with the same frequency — James
– James, Commented Aug 3, 2017 at 15:48
Logic for 1,2,3 seem off to me.... why not say if < .33, <.66 — epascarello
– epascarello, Commented Aug 3, 2017 at 15:49

epascarello · Accepted Answer · 2017-08-03 16:03:39Z

1

The reason why your code has so many ties is your distribution is really messed up.

isMultipleOf = function(number) {
  if (number % 2 === 0) {
    return 1;
  }
  if (number % 3 === 0) {
    return 2;
  } else {
    return 3;
  }
};

var results = [0,0,0];
for (var i=1; i<=100; i ++ ){
   results[isMultipleOf(i)-1] += 1
}

console.log(results)

Chance of 1: 50
Chance of 2: 17
Chance of 3: 33

If you want better results, than just use random and divide it into 3 parts.

getNum = function(number) {
  if (number < .33) {
    return 1;
  }
  if (number < .67) {
    return 2;
  } else {
    return 3;
  }
};

var results = [0,0,0];
for (var i=1; i<=100; i ++ ){
   var rn = Math.random()
   results[getNum(rn)-1] += 1
}

console.log(results)

answered Aug 3, 2017 at 16:03

epascarello

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Comments

James · Accepted Answer · 2017-08-03 16:07:15Z

Currently you select a random number from 1 to 100, select another random number less than or equal to the first, and then if the second number is a multiple of 2 return 1, multiple of 3 but not 2 return 2, else return 3.

Why not just pick two random numbers between 1 and 3?

var rnd = Math.floor(Math.random() * 3) + 1;  // 1 2 or 3, with 1/3 probability

Another option is for each of the numbers to be drawn from a known pool (like a lottery), guaranteeing there are no ties.

//start with an ordered array
var nums = [1,2,3];

// fisher-yates shuffle
for (var i=nums.length - 1; i > 0; i--) {
  var r = Math.floor(Math.random() * (i + 1));
  var tmp = nums[r];
  nums[r] = nums[i];
  nums[i] = tmp;
}

// any two elements can be our drawn numbers
alert("first: " + nums[0] + ", second: " + nums[1]);

Adrian Sawicki · Accepted Answer · 2017-08-03 15:51:59Z

0

First of all, do you want to have a draw or maybe it's better just to make another randomization when you have it until there will be winning side or just make it another time to lower chances for a draw? The easiest way would be of course adding more number so statistically there would be fewer chances for a draw.

answered Aug 3, 2017 at 15:51

Adrian Sawicki

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1 Comment

Nick Over a year ago

I was trying to add more numbers with my code, cause the idea behind was that the more random number i've got the less chances of a draw. It can be possible, but now it can happen 5-6 times in a row which i don't really like

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