Counter in an if/else statement using R?

Question

I am relatively new to R and programming in general and I was wondering if there is a way to put a counter inside of an if else statement in my for loop. I have the following if/else statement inside of a for loop:

if(runif(1)<min(1,r)) {
Gibbsalph[,t]=alphcandidate
} else{
Gibbsalph[,t]=Gibbsalph[,t-1]
}

Is there a way to count how many times the loop chose the "if" option (i.e. how many times Gibbsalph[,t]=alphcandidate) while proceeding through the iterations?

Thanks a lot!

score 3 · Accepted Answer · edited May 23 '17 at 12:24

3

This might be useful as it avoids creating the global variable i. see Examples of the perils of globals in R and Stata

init.counter <- function(){
  x <- 0
  function(){
    x <<- x + 1
    x
   }
}  #source: hadley wickham

> counter1 <- init.counter()
> 
> counter1()
[1] 1
> counter1()
[1] 2
>

To access the value of the counter without iterating it:

environment(counter1)$x

So it would end up as:

counter2 <- init.counter()
if(runif(1)<min(1,r)) {
counter2()
Gibbsalph[,t]=alphcandidate
} else{
Gibbsalph[,t]=Gibbsalph[,t-1]
}
environment(counter2)$x

edited May 23 '17 at 12:24

Community

1
1

answered Jan 22 '13 at 19:25

Michael

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Thanks for taking the time to write this up, this is excellent. The link you posted was helpful to me as well. I will definitely take that into account as I do my further programming! – user1836894 Jan 22 '13 at 20:50
Nice use of a lexical closure. – Clayton Stanley Jan 24 '13 at 06:13

score 0 · Answer 2 · answered Jan 22 '13 at 19:47

Here's what you've got now:

if(runif(1)<min(1,r))

Assuming your loop is over the sequence jj = 1:t , how about:

alltests <- runif(t) < min(1,r)  #vector of TRUE, FALSE
wincount <- sum(alltests)

and inside the loop,

Gibbsalph[,t] <- alphcandidate * alltests[jj] + Gibbsalph[,t-1]*(!alltests[jj])

Counter in an if/else statement using R?

2 Answers2