Creating a function message in R that tests if the input is a string

Question

I want to make a message in my function that tells the user to pass in the argument as a string, that is if they forget the quotation marks then the message should say "use quotation marks" and not "object X not found". Is that possible?

print_name <- function(name){
  if (!is.character(name)){
    stop("Name should be a character")
  }
  else {
    print(name)
  }
}

print_name(david)
#> Error in print_name(david): object 'david' not found

print_name("david")
#> [1] "david"

^{Created on 2019-05-24 by the reprex package (v0.2.1)}

Gregor Thomas · Accepted Answer · 2019-05-24 11:02:08Z

4

We can use tryCatch

print_name <- function(name){
   tryCatch({
     if (is.character(name))
       print(name)
     else
       print("not a character")
    }, error = function(e) {
    stop("Name should be a character - use quotes!")
  })
}

and then run the function

print_name(david)

Error in value[3L] : Name should be a character - use quotes!

print_name("david")
#[1] "david"

print_name(2)
#[1] "not a character"

edited May 24, 2019 at 11:02

Gregor Thomas

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answered May 24, 2019 at 10:56

Ronak Shah

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1 Comment

Ronak Shah Over a year ago

@David It's a variable to catch the error message. If you print e$message in the error function you will get the actual error message (in this case object 'david' not found) so that you can take actions based on that if required.

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