Groovy precedence issue

Question

I'm implementing a weighted lottery in groovy. It allows some participants to have a better chance at winning than others (basically exactly like the NBA draft). It works by tossing each participant into an array N times where N is the number of chances you have to win. It then picks a random index from that array.

Like a good little coder, I wrote a test. It picks a winner from the group 100 times and outputs how many times each participant was picked. The expectation being that it would fall roughly in line with how many times they should be picked (based on their number of chances). The results were...off.

I narrowed the issue down to a single line that, if split into 2 separate statements, works perfectly. A slimmed down version of the routine is below. The "bad" version is active and the "good version" is commented out

def randomInRange(int min, int max) { 
       Random rand = new Random()
       rand.nextInt((max - min) + 1) + min
}

def bob = [name:'bob', timesPicked:0]
def joe = [name:'joe', timesPicked:0]
def don = [name:'don', timesPicked:0]

def chanceWheel = []

//don should get picked a lot more
2.times{chanceWheel << bob}
2.times{chanceWheel << joe}
6.times{chanceWheel << don}

//pick somebody at random from the chance wheel 
100.times{
    //this will produce timesPicked counts that do NOT sum to 100 and usually under-represents don
    chanceWheel[randomInRange(0,9)].timesPicked++

    //splitting the logic into 2 lines will always have the correct sum of timesPicked with roughly the right distribution of winners
    //def picked = chanceWheel[randomInRange(0,9)] 
    //picked.timesPicked++
}

println bob
println joe
println don

My question is what is wrong with the one liner version? My guess is that its an order of execution issue but I cannot for the life of my figure out where its going off the rails.

Answer 1

chanceWheel[randomInRange(0,9)].timesPicked++ 

is

chanceWheel[randomInRange(0,9)].timesPicked = 
    chanceWheel[randomInRange(0,9)].timesPicked + 1 

which calls randomRange() twice in contrast to the working example where it is called once and assigned to a variable.