CODEWITHSUNDEEP
rtry-catch
Ricecakes
Ricecakes

Reputation: 781

TryCatch not printing warning unless warning is wrapped in ()

TryCatch is not printing the warnings unless the warning is wrapped in between brackets.

tryCatch(
  {
  print(wd)
},
error=function(e){
 (warning(sprintf('Watch out %s',e)))}
)

prints the warning ""Watch out Error in print(wd): object 'wd' not found\n"

but 

tryCatch(
   {
 print(wd)
    },
    error=function(e){
     warning(sprintf('Watch out %s',e)) }
    )

does not.

Any idea why? How can I fix this? This example is a minimal example. I have a much bigger function that runs through a loop and I don't necessarily want to stop the loop if there is an error but I want to see the warnings.

Upvotes: 0

Views: 121

Answers (1)

Luke Tierney
Luke Tierney

Reputation: 1055

For your loop you probably want to use message or cat, e.g.:

for (i in 1:2)
    tryCatch(print(wd),
             error = function(e) message(sprintf('Watch out %s',e)))
## Watch out Error in print(wd): object 'wd' not found
## 
## Watch out Error in print(wd): object 'wd' not found

To understand what is happening in your two versions:

  • warning does not print anything. It signals a warning, which a handler might print immediately or arrange to be printed later.

  • If a handler does not execute a non-local transfer of control, e.g. to a tryCatch, then ?warning says this about the value it returns:

Value:

The warning message as ‘character’ string, invisibly.

  • If an expression returns a result invisibly, then enclosing it in parentheses makes the result visible. Help files often use the idiom

    (x <- foo(y))

    to make the result of the assignment visible and have the top level print it.

Upvotes: 1

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