CODEWITHSUNDEEP
rtry-catch
Dmitriy
Dmitriy

Reputation: 939

How to create try-error class in R

I need to return "try-error" class or same class which inherits from it. Is it possible in R?

So, is it possible to create function like this:

Foo <- function(x)
{
    if (x != 2) { res <- 1 }
    else { res <- # create object with class type "try-error" and message "I hate 2!"/ }

    return(res);
}

Upvotes: 0

Views: 2247

Answers (2)

Roland
Roland

Reputation: 132676

Why don't you use try?

Foo <- function(x)
{ res <- try({
    if (x == 2L) stop("I hate 2!", call. = FALSE)
    1
  }) 
  res
}

Foo(2)
#Error : I hate 2!
#[1] "Error : I hate 2!\n"
#attr(,"class")
#[1] "try-error"
#attr(,"condition")
#<simpleError: I hate 2!>

I can't see a good reason why you'd create an object of class "try-error" manually.

Upvotes: 2

nrussell
nrussell

Reputation: 18602

Classes are a pretty loose concept in R; you can just assign any class(es) you desire as character strings in the class attribute of an object. For example, using the structure function: 

Foo <- function(x) {
    if (x != 2) {
        res <- 1
    } else { 
        res <- structure(
            "message", 
            class = c("try-error", "character")
        )
    }
    res
}

Foo(1)
# [1] 1

Foo(2)
# [1] "message"
# attr(,"class")
# [1] "try-error" "character"

class(Foo(2))
# [1] "try-error" "character"

Alternatively, you could use 

res <- "message"
class(res) <- c("try-error", class(res))

in place of structure.

It's usually a good idea to add new classes rather than completely overwrite the old classes so that method dispatch works reasonably, but depending on your use case this may not be needed or desired.

Upvotes: 4

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