[R] R and Matlab

[Claudia Beleites]

Dear Henrik,

sorry for bothering you with a report hastily pasted together and not 
particularly nice for you as I used my toy data flu from a non-standard package. 
I should have better used e.g. the iris.

I'm aware that writeMat doesn't deal with S4 objects. In fact, if I'd overlook 
the error message, there's the 2nd chance to see that the file size is 0B.
In fact the attempt to save flu directly was a classical "autopilot" error, 
that's why I tried to save the x afterwards.

So the problem here was the unnamed storing of x.

> I intentionally do not try to "infer" the name "x" from
> writeMat("flu.mat", x), basically because I think using substitute()
> should be avoided as far as possible, but also because it is unclear
> what the name should be in cases such as writeMat("flu.mat", 1:10).
I was just going to suggest a patch that assigns the names of type Vnumber to 
the unnamed objects - but when I wanted to get the source I realized your 
version with the warning is already out.

I think, however, you may forgot a nchar?: any (nchar (names) == 0)

So here's my suggestion for l. 775-777 of writeMat.R:

   if (is.null(names) || any (nchar (names) == 0L)) {
     names [nchar (names) == 0L] <- paste ("V", which (nchar (names) == 0L), sep 
= "")
     names (args) <- names
     warning("All objects written have to be named, e.g. use writeMat(..., x=a, 
y=y) and not writeMat(..., x=a, y): ", deparse(sys.call()), "\nDummy names have 
been assigned.");
   }


After all, e.g. data.frame () will also rather create dummy names for unnamed 
columns. And, I think, a warning should make the user aware that he's doing 
something that _may_ not work out as intendet. But here I think it is _most 
likely_ not working as intended.


> MISCELLANEOUS:
> Note that writeMat() cannot write compressed MAT files.  It is
> documented in help("readMat"), and will be so in help("writeMat") in
> the next release.  Package Rcompression, loaded or not, has no effect
> on writeMat().  It is only readMat() that can read them, if
> Rcompression is installed.  You do not have to load it
> explicitly/yourself - if readMat() detects a compress MAT file, it
> will automatically try to load it;
OK, good to know.

Thanks a lot for your explanation in spite of my bad report.

Claudia


-- 
Claudia Beleites
Dipartimento dei Materiali e delle Risorse Naturali
Università degli Studi di Trieste
Via Alfonso Valerio 6/a
I-34127 Trieste

phone: +39 0 40 5 58-37 68
email: cbeleites at units.it