R - checking the existence of objects in a function

Question

Suppose I have a set of variables x, ythat may or may not be defined. These variables are passed to a function with a name test.

y <- 10
test <- function(a,b) { ifelse(a > b, "hello", "world") }
test(x,y)

# Error in ifelse(a > b, "hello", "world") : object 'x' not found

If I called test(x,y)when x was not created, R will throw an error "object" x "not found".

If I add to the check for availability, the function works when called from a global environment

y <- 10
test <- function(a,b) { 
     print(exists(as.character(substitute(a))))
     if (!exists(as.character(substitute(a)))) {a <- 0}
     ifelse(a > b, "hello", "world")  
}
test(x,y)

# [1] FALSE
# [1] "world"

x <- 11
test(x,y)

[1] TRUE
[1] "hello"

However, if I complete test(x,y)inside the function blah. It cannot find an existing variable.

rm(list=ls())
test <- function(a,b) { 
     print(exists(as.character(substitute(a))))
     if (!exists(as.character(substitute(a)))) {a <- 0}
     ifelse(a > b, "hello", "world")  
}
blah <- function() { x <- 11; y <- 10; test(x,y)}
blah()
[1] FALSE -- expecting TRUE
[1] "world" -- expecting "hello"

I suppose the failure is due to the fact that he is not looking into the right environment. Any idea how I can get this to work correctly?

Answer 1

, :

test <- function(a,b) { 
     print(exists(as.character(substitute(a)), envir=parent.frame()))
     if (!exists(as.character(substitute(a)), envir=parent.frame())) {a <- 0}
     ifelse(a > b, "hello", "world")  
}

:

y <- 10
test(x,y)

# [1] FALSE
# [1] "world"

x <- 11
test(x,y)

#[1] TRUE
#[1] "hello"

rm(list=ls())

test <- function(a,b) { 
     print(exists(as.character(substitute(a)), envir=parent.frame()))
     if (!exists(as.character(substitute(a)), envir=parent.frame())) {a <- 0}
     ifelse(a > b, "hello", "world")  
}
blah <- function() { x <- 11; y <- 10; test(x,y)}
blah()

#[1] TRUE
#[1] "hello"