While loop that stores values in a vector and stops when a value is already in the vector [R Program-CodePudding

I have a function, say fun(x), this function calculates a value and returns it. Then, using the returned value, run the function fun(x) with that value. I would like to code a while loop that uses this function, to generate values and store them in a vector, until the generated value from the function has already appeared in the vector.

This is what I have attempted.

x <-1 #initial value to run the function with
vec <-numeric(100) #create an empty vector to store the values
k <- 0 # have a counter for the vector position

while((fun(x) %in% vec) != TRUE){ #this while loop with run until the value from the function is already in the vector
  k<- k  1 #increase counter 
  vec[k] <- fun(x) #run the function, store that value
  x <- vec[k] #set x as the stored value 
  
}

I cannot seem to figure out how to code this properly. Any help is appreciated

CodePudding user response：

Something like this? Obviously sample() will return different numbers in the while statement than in the loop, but I assume your function isn't random?

sample(1:10,1)
vec <- c() ## empty vector
x=10
while(!sample(1:x,1) %in% vec){
  x=sample(1:x,1)
  vec <- c(vec,x)
}

CodePudding user response：

Here is a way. It calls the function only once per iteration, saving its value in an auxiliary variable y. There is also a stop condition when the vector is full.
The function fun is an example meant for tests only returning one Poisson random number.

I have changed the starting value to x <- 10.

fun <- function(x) rpois(1, x)

x <- 10           # initial value to run the function with
n <- 100L         # results vector length
vec <- numeric(n) # create an empty vector to store the values
k <- 0L           # have a counter for the vector position
while(!((y <- fun(x)) %in% vec) && k < n){
  k <- k   1L
  vec[k] <- y
  x <- y
}
vec