round() ignores missing arguments if it is used inside another function where some arguments are missing.
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
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