If value exists in environment

Question

Is there a way how to check if value exists in R environment and if == TRUE, assign this existing value otherwise assign something else?

In other words, I have nothing in my R right now and I created this if else statement.

test <- if_else(exists("my_value"), my_value, "my value missing, assigning this string")

Result of

 exists("my_value")

is:

exists("my_value")
[1] FALSE

But once I run whole code I get this

Error in if_else(exists("my_value"), my_value, "my value missing, assigning this string") : object 'my_value' not found

Try doing `ls()`. It will show you all objects you have defined in your global env. — Sotos, Jul 02 '19 at 09:03
if `my_value` does not exist, after your statement, `test` will exist but `my_value` still won't — Cath, Jul 02 '19 at 09:08
This isn't really a duplicate, since the problem here is that OP is misusing `if_else` — Hong Ooi, Jul 02 '19 at 09:21
@HongOoi true, I reopened, though title is misleading imo. also, as `if_else` is not base R, tag of corresponding package should be included.... — Cath, Jul 02 '19 at 09:40
I guess the question is "how do I do this with `dplyr::if_else`?" — zx8754, Jul 02 '19 at 09:53
@zx8754 The answer should be "use `if() ... else ...`", since that is the control flow statement, not ifelse or if_else. — Hong Ooi, Jul 02 '19 at 10:41
@HongOoi Yes, agree, I was just composing the answer. Internet failed on me... so a bit of a delay. — zx8754, Jul 02 '19 at 10:49

score 3 · Answer 1 · answered Jul 02 '19 at 10:48

if() {} else {} is more suitable for this case:

if(exists("my_value")){ 
  test <- my_value } else { 
    test <- "my value missing, assigning this string"}

Using dplyr::if_else(condition, true, false, missing = NULL) won't work as it is checking the values for true and false are of the same length, class, type, hence the error.

I am guessing it could be done with if_else, if we manage to make values for true and false of the same class somehow.

If value exists in environment

1 Answers1