On 08/11/2021 11:48 a.m., Avi Gross via R-package-devel wrote:
Vincent,
But is the second being ignored the right result?
In many programming situations, subsequent assignments replace earlier ones.
And consider the way R allows something like this:
func(a=2, b=3, a=4, c=a*b)
Is it clear how to initialize the default for c as it depends on one value
of "a" or the other?
That c=a*b only works with non-standard tidyverse evaluation. It causes
other problems, e.g. the inability to pass ... properly (see
https://github.com/tidyverse/glue/issues/231 for an example).
Duncan Murdoch
Of course, you could just make multiple settings an error rather than
choosing an arbitrary fix.
R lists are more like a BAG data structure than a SET.
-----Original Message-----
From: R-package-devel <r-package-devel-boun...@r-project.org> On Behalf Of
Vincent van Hees
Sent: Monday, November 8, 2021 11:25 AM
To: Duncan Murdoch <murdoch.dun...@gmail.com>
Cc: r-package-devel@r-project.org
Subject: Re: [R-pkg-devel] R feature suggestion: Duplicated function
arguments check
Thanks Duncan, I have tried to make a minimalistic example:
myfun = function(...) {
input = list(...)
mysum = function(A = c(), B= c()) {
return(A+B)
}
if ("A" %in% names(input) & "B" %in% names(input)) {
print(mysum(A = input$A, B = input$B))
}
}
# test:
myfun(A = 1, B = 2, B = 4)
[1] 3
# So, the second B is ignored.
On Mon, 8 Nov 2021 at 17:03, Duncan Murdoch <murdoch.dun...@gmail.com>
wrote:
On 08/11/2021 10:29 a.m., Vincent van Hees wrote:
Not sure if this is the best place to post this message, as it is
more
of a
suggestion than a question.
When an R function accepts more than a handful of arguments there is
the risk that users accidentally provide arguments twice, e.g
myfun(A=1, B=2, C=4, D=5, A=7), and if those two values are not the
same it can have frustrating side-effects. To catch this I am
planning to add a check for duplicated arguments, as shown below, in
one of my own functions. I am
now
wondering whether this would be a useful feature for R itself to
operate
in
the background when running any R function that has more than a
certain number of input arguments.
Cheers, Vincent
myfun = function(...) {
#check input arguments for duplicate assignments
input = list(...)
if (length(input) > 0) {
argNames = names(input)
dupArgNames = duplicated(argNames)
if (any(dupArgNames)) {
for (dupi in unique(argNames[dupArgNames])) {
dupArgValues = input[which(argNames %in% dupi)]
if (all(dupArgValues == dupArgValues[[1]])) { # double
arguments,
but no confusion about what value should be
warning(paste0("\nArgument ", dupi, " has been provided
more
than
once in the same call, which is ambiguous. Please fix."))
} else { # double arguments, and confusion about what value
should
be,
stop(paste0("\nArgument ", dupi, " has been provided more
than once in the same call, which is ambiguous. Please fix."))
}
}
}
}
# rest of code...
}
Could you give an example where this is needed? If a named argument
is duplicated, R will catch that and give an error message:
> f(a=1, b=2, a=3)
Error in f(a = 1, b = 2, a = 3) :
formal argument "a" matched by multiple actual arguments
So this can only happen when it is an argument in the ... list that is
duplicated. But usually those are passed to some other function, so
something like
g <- function(...) f(...)
would also catch the duplication in g(a=1, b=2, a=3):
> g(a=1, b=2, a=3)
Error in f(...) :
formal argument "a" matched by multiple actual arguments
The only case where I can see this getting by is where you are never
using those arguments to match any formal argument, e.g.
list(a=1, b=2, a=3)
Maybe this should have been made illegal when R was created, but I
think it's too late to outlaw now: I'm sure there are lots of people
making use of this.
Or am I missing something?
Duncan Murdoch
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