Percentage Distribution of numbers in AS3 - actionscript-3

Question

I need to generate 238 numbers, with a range of 1-4, but I want to weight them, so there's say 35% chance of getting 3, 28% chance of getting 2, 18% chance of getting 4m, and 19% chance of getting 1.
I found this..
def select( values ):
variate = random.random() * sum( values.values() )
cumulative = 0.0
for item, weight in values.items():
cumulative += weight
if variate < cumulative: return item
return item # Shouldn't get here, but just in case of rounding... print select( { "a": 70, "b": 20, "c": 10 } )
But I don't see how to convert that to AS3?

Answer 1

I would do something like this:
var values:Array = [1,2,3,4];
var weights:Array = [35, 28, 18, 19];
var total:Number = 0;
for(var i in weights) {
total += weights[i];
}
var rndNum:Number = Math.floor(Math.random()*total);
var counter:Number = 0;
for(var j:Number = 0; j<weights.length; j++) {
counter += weights[j];
if( rndNum <= counter ) return values[j]; //This is the value
}
(untested code, but the idea should work)

Answer 2

Take a look at this article:
http://uihacker.blogspot.com/2009/09/actionscript-3-choose-random-item-from.html
You can also use Rnd.bit() to get a weighted 1 or 0 and adapt it to your situation.

Answer 3

Here for you:
/**
* random due to weighted values
*
* #param {{}} spec such as {'a':0.999, 'b':0.001}
* #return {*} return the key in object
*/
public static function weightedRand(spec:Object):* {
var i:String, j:int, table:Array = [];
for (i in spec) {
// from: https://stackoverflow.com/questions/8435183/generate-a-weighted-random-number
// The constant 10 below should be computed based on the
// weights in the spec for a correct and optimal table size.
// E.g. the spec {0:0.999, 1:0.001} will break this impl.
for (j=0; j<spec[i]*10; j++) {
table.push(i);
}
}
return table[Math.floor(Math.random() * table.length)];
}
Then you could test with this code:
public static function main():void {
// test calculate weighted rand
// random weighted
var result:Array = [];
for (var k:int = 0; k < 100; k++) {
var rand012:String = MyUtil.weightedRand({'y': 0.8, 'n1': 0.1, 'n2': 0.1});
result.push(rand012); // random in distribution...
}
logger.traceObject('result: ', result);
// counts
var counts:Object = {};
var totalCounts:int = 0;
for (var i:int = 0; i < result.length; i++) {
counts[result[i]] = 1 + (counts[result[i]] || 0);
totalCounts++;
}
logger.traceObject('counts: ', counts);
// ratios
var ratios:Object = {};
for (var c:String in counts) {
ratios[c] = counts[c] / totalCounts;
}
logger.traceObject('ratios: ', ratios);
}