R-alpha: generic write()

[Ross Ihaka]

Kurt Hornik writes:

>  Attached is a first shot at a generic write with my `old' write.table as
>  write.data.frame, suitably modified.  There is also a stupid generic
>  latex function, which is just there because it illustrates that the
>  extra arguments sep and eol are useful.
>
>  In playing with it, I noticed a few `problems'.
>
>  * The documentation for factor() says,
>
> 	If exclude is set to a zero length vector, then any NA values in
> 	x are used for form a new level for the factor.  This means that
> 	there will be no NA values in the result.
>
>  Perhaps I don't really understand this, but
>
>  R> x <- factor(c(1:3, NA), exclude=numeric(0))
>  R> x
>  [1]  1  2  3 NA
>  R> levels(x)
>  [1] "1" "2" "3"

Looks like a bug to me ...

>  * coerce.c has two error messages of the form
>
> 	error("use \"factor\", \"ordered\", \"cut\" or \"code\" to create factors\n");
>
>  but there is no function `code'.

A VERY old (pre- 0.1) error message

>  * cat() is a bit inconsistent:
>
>  R> cat(x, sep = "&")
>  1&2&3&4R> cat(x, sep = "&\n")
>  1&
>  2&
>  3&
>  4
>  R>
>
>  Actually, a final newline is added whenever sep contains a newline.
>  >From src/main/builtin.c:
>
>         nlsep = 0;
>         for (i = 0; i < LENGTH(sepr); i++)
>                 if (strstr(CHAR(STRING(sepr)[i]), "\n")) nlsep = 1;
>
> 	...
>
>         if ((pwidth != INT_MAX) || nlsep)
>                 Rprintf("\n");
>
>  I am not sure this is the right thing to do.
>
>  (In particular, it makes it rather messy to incrementally build data
>  files with `explicit' end-of-line strings (such as "\\") by appending
>  via cat().)
 
I will look at this a bit more (and compare with the AT&T prototype).

	Ross
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