[Rcpp-devel] indexing matrix by row names and column names

[Dirk Eddelbuettel]

On 2 March 2011 at 12:18, Mahdi Shafiei wrote:
| Hello,
| In R, one can define a matrix and assign names to tows and columns:
| 
| A = matrix(1:9, nrow=3, ncol=3);
| rownames(A) = c("R1", "R2", "R3")
| colnames(A) = c("C1", "C2", "C3")
| 
| and then access entries in A by these row and column names instead of row and
| column numbers like:
| 
| A["R1", "C1"]
| 
| I tried to find out if this is possible in some way in Rcpp for Matrix type. I
| know that one can set rownames and colnames attributes for an object of type
| Matrix but my understanding is that this is done for preparing an object to be
| passed to R.
| 
| Is there a way to retrieve entries of a let say NumericMatrix by row and column
| names  ?

You can certainly created named vectors, lists, ... etc so that they arrive
in R the proper way.  And you certainly index list elements by name as we do
that all the time for parameter values passed in, eg in RQuantLib I do

RcppExport SEXP EuropeanOption(SEXP optionParameters) {

    try {

        Rcpp::List rparam(optionParameters);    	// Parameters via R list object

        std::string type     = Rcpp::as<std::string>(rparam["type"]);
        double underlying    = Rcpp::as<double>(rparam["underlying"]);
        double strike        = Rcpp::as<double>(rparam["strike"]);
        QuantLib::Spread dividendYield = Rcpp::as<double>(rparam["dividendYield"]);
        QuantLib::Rate riskFreeRate    = Rcpp::as<double>(rparam["riskFreeRate"]);
        QuantLib::Time maturity        = Rcpp::as<double>(rparam["maturity"]);
        int length           = int(maturity*360 + 0.5); // FIXME: this could be better
        double volatility    = Rcpp::as<double>(rparam["volatility"]);

and there are more examples in the other packages using Rcpp.

Now, for NumericMatrix and friends: dunno. When I have a question like this I
start by looking (or grep'ing) around the unitTests directory...

Dirk
| 
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-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com