R - check if a variable exists

Question

I thought I had figured this one out. I have a variable called:

count_1

It's just a vector with one element. As I go through my loops, sometimes it has a value, and at other times it doesn't. All I want to do is ask if it contains anything, and if not, merely loop back around. Right now my script fails because when count_1 is empty, I get this:

missing value where TRUE/FALSE needed Execution halted

Here is my attempt so far:

if (exists("count_1"))
  { 
    #code#
  }

Answer 1

Use if(length(count_1) == 1) { next } to check if there is a value in count_1.

However, this will only work if your code does something like this:

dat <- 1:5
count_1 <- which(dat > 10)
count_1
# integer(0)
length(count_1) == 1
# [1] FALSE

It will not work with another way of filling the variable, e.g.:

count_1 <- ifelse(any(dat > 10), which(dat > 10), NA)
count_1
# [1] NA
length(count_1) == 1
# [1] TRUE

Answer 2

For a different reason, I need to check if a variable exists inside a function. I use this:

check=function(x) tryCatch(if(class(x) == 'logical') 1 else 1, error=function(e) 0) 
varX=1 
check(varX)
[1] 1
rm(varX)
check(varX)
[1] 0
f1= function(x) if(check(x)) cat('exists') else cat('not exists')
f1(varX)
not exists