[Rd] sprintf, check number of parameters

[Matthias Gondan]

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)

3. From the conversation below, it seems that this also raises a warning (in R-devel):
sprintf('%1$i', 1, 2)

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$.

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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