[R] printing reals from C with digits -- once more

[Ott Toomet]

Thank for Brian D. Ripley for the answer to my previous question.  

My aim is to print single values from different real vectors with
different digits option.  This is quite a possible with Rprintf() but
that one supprots printing format as C does, not in R native way
(setting digits=7 or printing with "%12.7f" are two quite different
things).  So I would like to find something more R-ish.

PrintValue() seems promising (it understands when I change
options(digits) but I did not get it to print a single value.  I tried

  SEXP variable;
  PrintValue(VECTOR_ELT(variable, i));

which lead to crash, while

  PrintValue(variable);

prints the whole vector.  

StringFromReal() (and printing as CHAR) is otherwise nice but I dont
know how can I make it to understand options(digits).


Can anybody suggest me a way for this?

Best wishes,

Ott


BTW, can I be sure that everything defined in /usr/lib/R/include and
R_ext are (more or less) safe to use?


 | From: Prof Brian D Ripley <ripley at stats.ox.ac.uk>
 | Date: Wed, 29 Jan 2003 09:01:44 +0000 (GMT Standard Time)
 | 
 | On Wed, 29 Jan 2003, Ott Toomet wrote:
 | 
 | > I want to print real numbers in C code with different values for
 | > digits.  How to do that?
 | 
 | Use Rprintf or PrintValue.  You'll need to work hard to convince me that
 | Rprintf is not adequate.
 | 
 | > As I have understood, what I should do is to call
 | >
 | > StringFromReal()
 | 
 | That's a coercion, not a printing routine.
 | 
 | > which calls FormatReal(), that one suggests the parameters (width,
 | > decimal places and exponential form).  FormatReal() includes
 | >
 | >     eps = pow(10.0, -(double)R_print.digits);
 | >
 | > So I guess I have to change the value of R_print.digits.
 | > R_print.digits is defined in include/Print.h in the package source,
 | > but unfortunately the installed version (in /usr/lib/R/include/R_ext) is
 | > quite a different.
 | 
 | R_ext/Print.h and Print.h are not the same thing: one is not a version of
 | the other.  The routines you mention are not documented in R-exts, and are
 | not part of the API.
 | 
 | > I guess that is because the structure is not meant
 | > to be accessible by user, although some system routines alter
 | > R_print.digits directly.
 | 
 | (Only the coercion and print routines!)
 | 
 | > So are there any good way to achieve it?
 | 
 | Temporarily change the options(digits) and call PrintValue().  You are not
 | meant to (and it is not safe to) mess with R's printing internals, and
 | these structures change even at patch releases.