[Rd] Fwd: Generating valid R code using R

[Peter Dalgaard]

"Henrik Bengtsson" <hb at stat.berkeley.edu> writes:

> Sorry, this question was supposed to go to r-devel; move it there now. /HB
> 
> ---------- Forwarded message ----------
> From: Henrik Bengtsson <hb at stat.berkeley.edu>
> Date: Jul 16, 2006 11:11 AM
> Subject: Generating valid R code using R
> To: R-help <r-help at stat.math.ethz.ch>
> 
> 
> Hi,
> 
> I'm trying to generate valid R code using R. Parts of the task is to
> read a sequence of characters from file and escape them such that they
> can be put in quotation marks to form a valid R code string.  Example:
> 
> Let the input file be (four rows containing ASCII 0-255 characters):
> abcdef<tab>ghijk\nlmno
> second row\t\a\\
> 
> fourth and so on...
> <EOF>
> 
> Now, find escapeString() such that the following piece of code
> generates a second file called 'file2.txt' which is identical to
> 'file1.txt':
> 
> inStr <- readChar("file1.txt", nchars=999)
> esStr <- escapeString(inStr)
> rCode <- sprintf('cat(file="file2.txt", "%s")', esStr)
> cat(file="foo.R", rCode)
> source("foo.R")
> 
> For instance, quotation marks has to be escaped in order for 'rCode'
> to be valid, same with newlines etc.  What's the best way to do this?
> Currently I use an ad hoc sequence of gsub() substitutions to do this,
> but is there a better way to create the 'rCode' string?

I'd look in the direction of deparse/dput, as in

> X
[1] "abc\t\nfoobar\"\n"
> cat(X)
abc
foobar"
> deparse(X)
[1] "\"abc\\t\\nfoobar\\\"\\n\""


-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
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