On Sat, 4 Jun 2005, James Bullard wrote:
Hi all, this should be a relatively straightforward question. I am
constructing an R list in C which will contain both Integers and Strings (by
string I mean in C I have const char* whose values I want passed through to
R) The Integers are easy. I do something like this:
PROTECT(tmp = NEW_INTEGER(1));
INTEGER(tmp)[0] = header.GetCols();
SET_STRING_ELT(names, i, mkChar(cols));
SET_VECTOR_ELT(vals, i++, tmp);
UNPROTECT(1);
This works just fine. So, when I wanted to set a string element of the list
(please correct my nomenclature if I am refering to things incorrectly) I
used the following bit of code:
SET_STRING_ELT(names, i, mkChar(header));
SET_VECTOR_ELT(vals, i++, mkChar(header.GetHeader().c_str()));
I did this based on the fact that this is how I have created named attributes
for lists in the past and it seemed to work fine, however in R when I call
the function I get the following results (sorry for the output, but I think
the important thing is the CHARSXP: ...).
$header
CHARSXP:
Cols=712\rRows=712\rTotalX=712\rTotalY=712\rOffsetX=0\rOffsetY=0\rGridCornerUL=162
119\rGridCornerUR=5286 153\rGridCornerLR=5253 5270\rGridCornerLL=130
5237\rAxis-invertX=0\rAxisInvertY=0\rswapXY=0\rDatHeader=[0..65528]
T1:CLS=5412 RWS=5412 XIN=2 YIN=2 VE=302.0 07/09/04 13:38:45
50101350 M10 \024 \024 Doe16s.1sq \024 \024 \024 \024 \024 \024
\024 \024 \024
6\rAlgorithm=Percentile\rAlgorithmParameters=Percentile:75;CellMargin:2;OutlierHigh:1.500;OutlierLow:1.004;AlgVersion:6.0;FixedCellSize:FALSE;IgnoreOutliersInShiftRows:FALSE;FeatureExtraction:FALSE;UseSubgrids:FALSE;RandomizePixels:FALSE;ErrorBasis:StdvMean;StdMult:1.00\r
A character vector is a STRSXP, so mkChar is not the right function.
Ok, so then I thought to try something a little closer to how I did the
INTEGER. So I used the following code:
PROTECT(tmp = NEW_CHARACTER(1));
CHAR(tmp)[0] = *header.GetHeader().c_str();
SET_STRING_ELT(names, i, mkChar(header));
SET_VECTOR_ELT(vals, i++, tmp);
UNPROTECT(1);
Which in R returns the following:
$header
[1]
So that is not working.
As STRSXPs are not structured identically to INTSXPs.
So the question is: given a function in C/C++ which
returns a const char* how do I correctly create an R character string/vector
(terminology?) to set as a list element. Thanks for any advice or any
particular parts of the R source tree which might be illuminating. Also, if
anyone knows some shorter code for the above code which sets the INTEGER
elements of the list that would be nice as well.
You want mkString, e.g.
SET_STRING_ELT(names, i, mkChar(header));
SET_VECTOR_ELT(vals, i++, mkString(*header.GetHeader().c_str()));
I would have written
PROTECT(tmp = NEW_INTEGER(1));
INTEGER(tmp)[0] = header.GetCols();
SET_STRING_ELT(names, i, mkChar(cols));
SET_VECTOR_ELT(vals, i++, tmp);
UNPROTECT(1);
as
SET_STRING_ELT(names, i, mkChar(cols));
tmp = allocVector(INTSXP, 1)
INTEGER(tmp)[0] = header.GetCols();
SET_VECTOR_ELT(vals, i++, tmp);
as no further allocation and hence no PROTECTion is required. You could
encapsulate it as a function (mkInt?) if you prefer.
--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UKFax: +44 1865 272595
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