[R] paste argument of a function as a file name

[Martin Maechler]

>>>>> "UweL" == Uwe Ligges <ligges at statistik.uni-dortmund.de>
>>>>>     on Thu, 10 Nov 2005 15:11:45 +0100 writes:

    UweL> Luis Ridao Cruz wrote:
    >> R-help,
    >> 
    >> I have a function which is exporting the output to a file via
    >> write.table(df, file =  "file name.xls" )
    >> 
    >> What I want is to paste the file name (above) by taking the argument to
    >> the function as a file name 
    >> 
    >> something like this:
    >> 
    >> MY.function<- function(df)
    >> {
    >> ...
    >> ...
    >> write.table(df,"argument.xls")
    >> }
    >> MY.function(argument)

    UweL> Has been asked hundreds of times on this list. 

indeed! ...  and, it seems, has been answered 200 times with
hints that I would consider "suboptimal" ..

    UweL> check the archives as the posting guide asks to do ...

    UweL> Hint: paste()

well, we know that that works;
however, since at least R version 1.0.0, there's the function 
file.path()  which is a simple wrapper for paste()  allowing a
slightly nicer syntax more readable and portable *) code.
So, we do recommend using   file.path()  as in

> list.files( file.path("C:", "WINDOWS", "system") )
or
> list.files( file.path("usr", "local", "lib"))

---

*) Though since nowadays the file separator "/" works on
   all current versions of R (I think),
   the trick of automatically using the correct file name separator
   for the given platform (namely  .Platform$file.sep )
   seems less important now.

Martin Maechler, ETH Zurich