On Fri, 2011-11-18 at 16:43 +0100, Joris Meys wrote:
> I have stumbled across some behaviour in R that I really can't place,
> and that makes coding a bit tricky. I know that I can work around it
> when explicitly checking for missing arguments, but still...
> I have two functions. I have a first function based on paste
>
> fun1 <- function(x,y){
> print(missing(y))
> paste(x,'X',sep=y)
> }
>
> If I try this function without specifying `y`, I get the (expected)
> error message:
>
> > fun1(letters[1:6])
> [1] TRUE
> Error in paste(x, "X", sep = y) :
> argument "y" is missing, with no default
>
> The second one with round :
> fun2 <- function(x,y){ print(missing(y)) round(x,digits=y) }
> If I try this function without specifying `y`, it works unexpectedly
> whereas it shouldn't :
> > fun2(100.1) [1] TRUE [1] 100
round() is implemented as:
> round
function (x, digits = 0) .Primitive("round")
using the .Primitive means of calling C code. `?.Primitve` refers you to
the R Internals manual, which basically states that how the compiled
functions should be called and number of arguments etc is stored in a
table. This table is given here:
http://svn.r-project.org/R/trunk/src/main/names.c
The relevant part of which is:
/* printname c-entry offset eval arity pp-kind precedence
rightassoc
* --------- ------- ------ ---- ----- ------- ----------
----------*/
....
/* Mathematical Functions */
/* primitives: these are group generic and so need to eval args (possibly
internally) */
{"round", do_Math2, 10001, 0, -1, {PP_FUNCALL, PREC_FN,
0}},
the eval column indicates features of how arguments are evaluated and
what have you. A value of 0 equates to 000 and the last 0 indicates
whether arguments are to be evaluated with 0 indicating no evaluation
and 1 evaluation.
round is indicated to not evaluate its arguments. I don't follow the C
code well enough to know if it should be catching the missing argument
further on - it must be because it is falling back to the default, but
the above explains that the not evaluating arguments is intended.
G
> In my view, fun1 should definitely give the error message as well, as
> it is not intended to have a default behaviour when y is missing.
> Still, the round() function ignores the fact y is missing. Is this by
> design, is there a check missing in round, or is something else going
> on that I am overlooking?
>
> Cheers
> Joris
> > sessionInfo()
> R version 2.14.0 (2011-10-31)
> Platform: i386-pc-mingw32/i386 (32-bit)
>
> locale:
> [1] LC_COLLATE=English_United Kingdom.1252
> [2] LC_CTYPE=English_United Kingdom.1252
> [3] LC_MONETARY=English_United Kingdom.1252
> [4] LC_NUMERIC=C
> [5] LC_TIME=English_United Kingdom.1252
>
> attached base packages:
> [1] stats graphics grDevices utils datasets methods
> [7] base
>
> loaded via a namespace (and not attached):
> [1] tools_2.14.0
>
--
%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
Dr. Gavin Simpson [t] +44 (0)20 7679 0522
ECRC, UCL Geography, [f] +44 (0)20 7679 0565
Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk
Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/
UK. WC1E 6BT. [w] http://www.freshwaters.org.uk
%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
