[R] Help with prob in sample()

[Thomas]

I'm trying to figure out exactly what the prob parameter in the sample  
function does.

With the following code, does sample look randomly for the first  
possible sample--let's say it choses the second element--and then  
assess whether it can be chosen according to it's probability which is  
0.8? It seems unlikely it would work like this.

Or does it create a `biased die' which in this case would have ten  
sides that each come up according to the probabilities in myProb, and  
roll it to see which is the first element chosen, then remove that  
element, create a new biased die with 9 sides and roll it again?

i <- c(1:10)
myProbs <- c(0.2, 0.8, 0.3, 0.2, 0.1, 0.1, 0.1, 0.2, 0.3, 0.4)
f <- sample(i,5, replace=FALSE, prob=myProbs)

Then what's the difference in terms of sampling between the following  
two examples, the second of which has been created so that the  
probabilities add to 1?

i <- c(1:10)
myProbs <- c(0.1, 0.1, 0.1, 0.1, 0.1, 0.9, 0.9, 0.9, 0.9, 0.9)
f <- sample(i,5, replace=FALSE, prob=myProbs)

i <- c(1:10)
myProbs <- c(0.1/5, 0.1/5, 0.1/5, 0.1/5, 0.1/5, 0.9/5, 0.9/5, 0.9/5,  
0.9/5, 0.9/5)
f <- sample(i,5, replace=FALSE, prob=myProbs)

Thank you,

Thomas Chesney
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