[R] Sweave & xtable [problem solved/workaround -> bug in xtable or textConnection?]

[Hedderik van Rijn]

> I'm trying to get Sweave running for automatic report generation, and 
> it seems to run fine when just using verbatim output. However, I've 
> ran into a problem with xtable.

A quick solution (as long as the table is not too wide) is to include 
the following code after library(xtable), replacing the original 
print.string

print.string <- function(x,...) {
   
lapply(strsplit(x$text,"\n")[[1]],cat,"\n",file=x$file,append=x$append)
   return(invisible())
}

The problem seems to be that textConnection() (used in the Sweave code) 
is not able to process the long strings that sometimes get sink'ed to 
it. When sending a string directly to it, a warning is triggered:

## Error/truncation with warning:
con <- textConnection("output","w");
sink(file=con);
paste(rep("123456789!",1000),collapse="");
## Warning message:
## line truncated in output text connection
sink()
rm(last.warning)

However, when a long string is send to textConnection via xtable, no 
warning is shown:

## Error/truncation without warning:
library("xtable")
con <- textConnection("output","w")
sink(file=con)
xtable(matrix(rnorm(1000),100))
sink()
## print(output) would show the truncated LaTeX table, warnings() 
doesn't show any warning

I'm not sure whether textConnection or xtable should be blamed, but 
changing the single cat() with the lapply/strsplit/cat combination in 
print.string solved the/my problem.

If the truncation of long strings is official/known behavior of 
textConnection, the following text in textConnection's help page might 
need some revision, i.e., some more explicit statement that long 
strings might get truncated. (And, maybe also a definition of what a 
"completed line of output" is, i.e., ending in a "\n".)

      An output text connection is opened and creates an R character
      vector of the given name in the user's workspace.  This object
      will at all times hold the completed lines of output to the
      connection, and `isIncomplete' will indicate if there is an
      incomplete final line.  Closing the connection will output the
      final line, complete or not.

   - Hedderik.

P.S. I've seen a lot of bus errors and segmentation faults while trying 
to find the cause of the problem. If anyone is interested, I can try to 
see if I can reproduce those. I'm using:

R : Copyright 2002, The R Development Core Team
Version 1.6.1  (2002-11-01)

% latex table generated in R 1.6.1 by xtable 1.0-11 package