[R] Testing for warning inside functions

[Peter Wolf]

Prof Brian Ripley wrote:

> On Wed, 18 May 2005, Peter Wolf wrote:
>
>> I am looking for a way to get a warning message
>> immediately after an evaluation within a function.
>> To get error messages you can use geterrmessage().
>
>
> Well, only in an error handler, as an error normally throws you out of 
> the function.  (That is the point of geterrmessage(), to enable error 
> handlers to be written.)
>
> To print the message immediately, look up options("warn").

options(warn=1) prints the message immediately,
but I cannot store it in a variable to analyse it or to show the message 
it in a message box, for example.

>   We don't have a general warnings handler mechanism, but you can make 
> use of condition objects. 

Thank you, I will have a look at condition objects.

>> But I found no function that allows me to check for
>> warnings.
>>
>> Five years ago this questions has been posted
>> but I haven't found any answer.
>
>
> What exactly is `this question'?  I see several assertions but no 
> question.  (It would have been helpful to give an exact reference to 
> the archives.)

link to the old mail: R-help archive Jan - June 2000:

* [R] Testing for warning inside functions -- V/idhyanath Rao (Sun 07 
May 2000 - 12:46:38 EST)/
Message-ID: <000301bfb831$33b87c60$d370fe8c at lucent.com>
"This is probably a newbie question: How do I test, inside a function, is
a call I made from inside that function produced a warning? ..."

>
>
>> Thanks for any help.
>>
>> Peter Wolf
>>
>>
>> ------------
>>
>> For illustration purpose a simple example follows:
>> you can get warnings after an error occured or after
>> exiting from the function but not at once after
>> "x<-matrix(1:3,2,2)":
>>
>>> options(warn=0)
>>> f<-function(x){
>>
>>  x<-matrix(1:3,2,2)
>>  print(0)
>>  warnings()  # no warning is shown
>>  print(1)
>>  try({xxx})
>>  print(2)
>>  print(geterrmessage())
>>  print(3)
>>  warnings()
>>  print(4)
>> }
>>
>>> f()
>>
>> [1] 0
>> [1] 1
>> Fehler in try({ : Objekt "xxx" nicht gefunden
>> Zusätzlich: Warnmeldung:
>> Datenlänge [3] ist kein Teiler oder Vielfaches der Anzahl der Zeilen 
>> [2] in matrix
>> [1] 2
>> [1] "Fehler in try({ : Objekt \"xxx\" nicht gefunden\n"
>> [1] 3
>> Warning message:
>> Datenlänge [3] ist kein Teiler oder Vielfaches der Anzahl der Zeilen 
>> [2] in matrix
>> [1] 4
>
>