Dear Matthias,
On 2/6/21 2:11 PM, Matthias Gondan wrote:
Dear developers,
This is a follow-up from an earlier mail about warnings of unused arguments in
sprintf:
1. This should obviously raise an error (and it does):
sprintf('%i %i', 1)
Fehler in sprintf("%i %i", 1) : zu wenig Argumente [= too few arguments]
2. This should, in my opinion, raise a warning about an unused argument (and I
think it does in now R-devel):
sprintf('%i', 1, 2)
yes, it does.
3. From the conversation below, it seems that this also raises a warning (in
R-devel):
sprintf('%1$i', 1, 2)
yes, it does as well
I think that one should be suppressed. When I reported this a few months ago, I
didn’t really have a use case for (3), but now I think I have found something.
Suppose I have a function that calculates some descriptive statistics, mean,
sd, available cases, missings, something like the one below:
msnx = function(x, mask='%1$.1f (SD=%2$.1f, n=%3$i, NA=%4$i)')
{
m = mean(x, na.rm=TRUE)
s = sd(x, na.rm=TRUE)
n = sum(!is.na(x))
na = sum(is.na(x))
sprintf(mask, m, s, n, na)
}
The mask is meant to help formatting it a bit.
msnx(T0)
[1] "30.7 (SD=4.7, n=104, NA=0)"
Now I want a „less detailed“ summary, so I invoke the function with something
like
msnx(T0, mask='%1$.1f (SD=%2$.1f)')
[1] "30.7 (SD=4.7)"
In my opinion, in the last example, sprintf should not raise the warning in (2)
if all arguments in the mask are „dollared“. I am still a bit unsure since the
example uses a function that calculate things that aren’t being used (n and
na), and this could be considered bad programming style. But there might be
other use cases, and it is, nevertheless, a deliberate choice to skip arguments
3$ and 4$.
Thanks for the example. I am sympathetic with your concerns about the
programming style in it: the caller needs to know exactly how "mask"
will be used, that it would be in a call to sprintf() and what would be
the indices of the arguments.
The warning has been introduced a while ago and there has not been any
report yet that it would break existing good style code (particularly
CRAN packages have been tested extensively), which indicates that
currently the R code base does not rely on unused $- arguments.
It is hence I think wise to keep the warning to prevent R code base from
relying on that in the future, because gcc/clang already warn on unused
$-arguments. Not only that gcc developers must have been thinking hard
about the same thing before us getting to this conclusion: $- arguments
are a POSIX extension and gcc/clang are the key compilers for POSIX
systems, so it is safer to abide by their rules. In principle POSIX may
mandate that $- arguments are used explicitly in the future (now it is
rather vague, it seems unused are fine only when last), and even if not,
deviations from gcc/clang could cause confusion for applications and
developers using both C/C++ and R.
Best
Tomas
Best wishes,
Matthias
Dear Matthias,
thanks for the suggestion, R-devel now warns on unused arguments by
format (both numbered and un-numbered). It seems that the new warning is
useful, often it finds cases when arguments were accidentally passed to
sprintf but had been meant for a different function.
R allows combining both numbered and un-numbered references in a single
format, even though it may be better to avoid and POSIX does not allow
that.
Best
Tomas
On 9/20/20 1:03 PM, Matthias Gondan wrote:
Dear R developers,
I am wondering if this should raise an error or a warning.
sprintf('%.f, %.f', 1, 2, 3)
[1] "1, 2"
I am aware that R has „numbered“ sprintf arguments (sprintf('%1$.f', …), and in
that case, omissing of specific arguments may be intended. But in the usual
syntax, omission of an argument is probably a mistake.
Thank you for your consideration.
Best wishes,
Matthias
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