multiple next statements in function - r

Question

I'm trying to run a function much more complex but equal to:
A <<- 5
B <<- 5
table <- data.frame(A,B)
backup <- table
test <- function(A,B){
while(A > 0){
r <- runif(1,0,1)
if ((r >= 0)&(r <= 0.5)){
A <- A + 1
B <- B - 1
} else if ((r > 0.5)&(r<=1)){
A <- A - 1
B <- B + 1
}
tab <- cbind(A,B)
table <<- rbind(table,tab)
if (nrow(table) == 10) {
break
} else if ((A > 0) & (nrow(table) != 10)) {
next
} else {if ((A == 0) & (nrow(table != 10)) { #pointing to error here?
A <- 5
B <- 5
table <- backup
next
}
}
}
So what I want this function to do is stop when the when number of rows of the table (= the number of times the function ran) is equal to a certain value, in this case 10. But A cannot take a value below 0. If A reaches 0 before the number of rows of the table is 10 the whole process has to start again, with the same inputvalues as before.
However, this function does not work. I think it's because I use multiple next statements, is that correct?
Thanks!

Answer 1

I think you're on the right track... just a few recommendations
I think this accomplishes what you're trying to achieve a little cleaner. I second Carl's suggestion of avoiding the global operator '<<-' when possible and passing the objects through to the function as arguments or parameters. I also second Justin's suggestion of avoiding the break command in favor of placing the return() call smartly. To accomplish this, I put your 10 (stopping criteria) directly into the while loop. I included it as a parameter n so that you can experiment with different stopping criteria. Hope this helps :)
test <- function(A,B,n){
A0 <- A
B0 <- B
tab <- data.frame(A,B)
while(A > 0 & nrow(tab) < n){
r <- runif(1,0,1)
if (r <= 0.5){
A <- A + 1
B <- B - 1
} else {
A <- A - 1
B <- B + 1
}
tab1 <- cbind(A,B)
tab <- rbind(tab,tab1)
if(nrow(tab)<n & A==0){
A<-5
B<-5
tab <- cbind(A0,B0)
names(tab) <- c('A', 'B')
print(paste('found A==0 in less than ', n, ' iterations', sep=''))
}
}
return(tab)
}
Testing function...
## running function
A <- 5
B <- 5
testDF <- test(A,B,10)
> testDF
A B
1 5 5
2 6 4
3 5 5
4 6 4
5 7 3
6 8 2
7 9 1
8 10 0
9 9 1
10 10 0