How to check if object (variable) is defined in R?

Question

I\'d like to check if some variable is defined in R - without getting an error. How can I do this?

My attempts (not successful):

> is.na(ooxx)
Err         


        

Answer 1

If you don't want to use quotes, you can use deparse(substitute()) trick which I found in the example section of ?substitute:

is.defined <- function(sym) {
  sym <- deparse(substitute(sym))
  env <- parent.frame()
  exists(sym, env)
}

is.defined(a)
# FALSE
a <- 10
is.defined(a)
# TRUE