R help - May 2007 - getting informative error messages

Certain errors seem to generate messages that are less informative than 
most -- they just tell you which function an error happened in, but 
don't indicate which line or expression the error occurred in.

Here's a toy example:

 > f <- function(x) {a <- 1; y <- x[list(1:3)]; b <- 2;
return(y)}
 > options(error=NULL)
 > f(1:3)
Error in f(1:3) : invalid subscript type
 > traceback()
1: f(1:3)
 >

In this function, it's clear that the error is in subscripting 'x',
but
it's not always so immediately obvious in lengthier functions.

Is there anything I can do to get a more informative error message in 
this type of situation?  I couldn't find any help in the section 
"Debugging R Code" in "R-exts" (or anything at all relevant
in "R-intro").

(Different values for options(error=...) and different formatting of the 
function made no difference.)

-- Tony Plate

 > sessionInfo()
R version 2.5.0 (2007-04-23)
i386-pc-mingw32

locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United 
States.1252;LC_MONETARY=English_United 
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252

attached base packages:
[1] "stats"     "graphics"  "grDevices"
"utils"     "datasets"  "methods"
[7] "base"

other attached packages:
tap.misc
    "1.0"
 >

Hi, Tony: 

      Are you familiar with the 'debug' command?  I agree that more 
informative error messages and 'traceback' would be nice, but I've
found
the 'debug' facility quite useful.  [I even sometimes prepare a shell of
a function 'fn', then say debug(fn) and fn(), and complete writing the 
function in its native environment where I can more easily check what 
each step does.]  I've heard that 'debug' does not work will with S4
class generics, but I have not so far had to deal with that.  {There is 
also a 'debug' package, which is completely separate from the debug 
command in the 'base' package.  I've heard that it has more
extensive
capabilities, but I've never used it.}

      I suspect you may already know 'debug', but for those who
don't, I
think it's worth noting its utility for this kind of thing. 

      Hope this helps. 
      Spencer Graves

Tony Plate wrote:
> Certain errors seem to generate messages that are less informative than 
> most -- they just tell you which function an error happened in, but 
> don't indicate which line or expression the error occurred in.
>
> Here's a toy example:
>
>  > f <- function(x) {a <- 1; y <- x[list(1:3)]; b <- 2;
return(y)}
>  > options(error=NULL)
>  > f(1:3)
> Error in f(1:3) : invalid subscript type
>  > traceback()
> 1: f(1:3)
>  >
>
> In this function, it's clear that the error is in subscripting
'x', but
> it's not always so immediately obvious in lengthier functions.
>
> Is there anything I can do to get a more informative error message in 
> this type of situation?  I couldn't find any help in the section 
> "Debugging R Code" in "R-exts" (or anything at all
relevant in "R-intro").
>
> (Different values for options(error=...) and different formatting of the 
> function made no difference.)
>
> -- Tony Plate
>
>  > sessionInfo()
> R version 2.5.0 (2007-04-23)
> i386-pc-mingw32
>
> locale:
> LC_COLLATE=English_United States.1252;LC_CTYPE=English_United 
> States.1252;LC_MONETARY=English_United 
> States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
>
> attached base packages:
> [1] "stats"     "graphics"  "grDevices"
"utils"     "datasets"  "methods"
> [7] "base"
>
> other attached packages:
> tap.misc
>     "1.0"
>  >
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

It is not clear to me what you want here.

Errors are tagged by a 'call', and f(1:3) is the innermost
'call' (special
primitives do not set a context and so do not count if you consider '[' 
to be a function).

The message could tell you what the type was, but it does not and we have 
lost the pool of active contributors we once had to submit tested patches 
for things like that.


On Mon, 7 May 2007, Tony Plate wrote:
> Certain errors seem to generate messages that are less informative than
> most -- they just tell you which function an error happened in, but
> don't indicate which line or expression the error occurred in.
>
> Here's a toy example:
>
> > f <- function(x) {a <- 1; y <- x[list(1:3)]; b <- 2;
return(y)}
> > options(error=NULL)
> > f(1:3)
> Error in f(1:3) : invalid subscript type
> > traceback()
> 1: f(1:3)
> >
>
> In this function, it's clear that the error is in subscripting
'x', but
> it's not always so immediately obvious in lengthier functions.
>
> Is there anything I can do to get a more informative error message in
> this type of situation?  I couldn't find any help in the section
> "Debugging R Code" in "R-exts" (or anything at all
relevant in "R-intro").
>
> (Different values for options(error=...) and different formatting of the
> function made no difference.)
>
> -- Tony Plate
>
> > sessionInfo()
> R version 2.5.0 (2007-04-23)
> i386-pc-mingw32
>
> locale:
> LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
> States.1252;LC_MONETARY=English_United
> States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
>
> attached base packages:
> [1] "stats"     "graphics"  "grDevices"
"utils"     "datasets"  "methods"
> [7] "base"
>
> other attached packages:
> tap.misc
>    "1.0"
> >
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595