Package 'RcppExamples'

Title: Examples using 'Rcpp' to Interface R and C++
Description: Examples for Seamless R and C++ integration The 'Rcpp' package contains a C++ library that facilitates the integration of R and C++ in various ways. This package provides some usage examples. Note that the documentation in this package currently does not cover all the features in the package. The site <https://gallery.rcpp.org> regroups a large number of examples for 'Rcpp'.
Authors: Dirk Eddelbuettel and Romain Francois
Maintainer: Dirk Eddelbuettel <[email protected]>
License: GPL (>= 2)
Version: 0.1.9.3
Built: 2024-06-21 05:15:26 UTC
Source: https://github.com/eddelbuettel/rcppexamples

Help Index


Examples for the Rcpp R/C++ Interface library

Description

This package shows some simple examples for the use of Rcpp.

It can also serve as a working template to create packages that use Rcpp to interface C++ code or libraries.

Details

The Rcpp package provides a number of C++ classes that ease access to C++ from R. This comprises both passing parameters to functions, as well as returning results back from C++ to R.

The RcppExamples package provides some simple examples for use of Rcpp. At this point the documentation is not complete in the sense of not covering all accessible classes. However, several basic use cases are illustrated,

Author(s)

Dominick Samperi wrote the initial versions of Rcpp (and RcppTemplate) during 2005 and 2006. Dirk Eddelbuettel made some additions, and became maintainer in 2008. Dirk Eddelbuettel and Romain Francois have been extending Rcpp since 2009.

See Also

The https://gallery.rcpp.org site regroups a number of examples.


Convert Index and String Vector into CharacterVector, and vice versa

Description

These two functions are an illustration of how as.character and as.factor may be reimplemented at the C++ level.

Usage

factor2char(iv)

char2factor(sv)

Arguments

iv

A Integer Vector corresponding to numeric representation of the factor This vector is also expected to have an attribute ‘levels’ with the factor levels

sv

A String Vector

Value

A Character Vector which at each position contains the level value of the corresponding index, or a Factor, depending on the function

Examples

f <- as.factor(c("red", "green", "blue", "red"))
factor2char(f);
f <- as.factor(c("red", "green", "blue", "red"))
v <- factor2char(f);
char2factor(v)

Rcpp::DataFrame example for Rcpp

Description

A DataFrame can be passed C++ and can be instantiated as a corresponding C++ object using the Rcpp API.

This example shows (in the corresponding C++ code) how to access, modify and create a data frame.

Details

Usage of Rcpp::DataFrame is fully defined in the respective header file.

The C++ source file corresponding to the this function does the following:

      // we receive a 'DF' data.frame object
      // and access each column by name
      Rcpp::IntegerVector a = DF["a"];
      Rcpp::CharacterVector b = DF["b"];
      Rcpp::DateVector c = DF["c"];
      
      // do something
      a[2] = 42;
      b[1] = "foo";
      c[0] = c[0] + 7;                      // move up a week

      // create a new data frame
      Rcpp::DataFrame NDF = 
	  Rcpp::DataFrame::create(Rcpp::Named("a")=a,
				  Rcpp::Named("b")=b,
				  Rcpp::Named("c")=c);

      // and return old and new in list
      return(Rcpp::List::create(Rcpp::Named("origDataFrame")=DF,
				Rcpp::Named("newDataFrame")=NDF));
  

Author(s)

Dirk Eddelbuettel and Romain Francois

Examples

## Not run: 
  RcppDataFrame()
  
## End(Not run)

C++ classes for interfacing date and datetime R objects

Description

Rcpp has the classes Rcpp::Date, Rcpp::Datetime, Rcpp::DateVector and Rcpp::DatetimeVector.

Details

In the C++ code for the RcppDateExample.cpp file:

        // [[Rcpp::export]]
        List DateExample(DateVector & dv, DatetimeVector & dtv) {
            Function formatDate("format.Date");
            Function formatDatetime("format.POSIXct");
            
            Rprintf("\nIn C++, seeing the following date value\n");
            for (int i=0; i<dv.size(); i++) {
                Rcout << as<std::string>(formatDate(wrap(dv[i]))) << std::endl;
                dv[i] = dv[i] + 7;		// shift a week
            }
            Rprintf("\nIn C++, seeing the following datetime value\n");
            for (int i=0; i<dtv.size(); i++) {
                Rcout << as<std::string>(formatDatetime(wrap(dtv[i]))) << std::endl;
                dtv[i] = dtv[i] + 0.250;    // shift 250 millisec
            }
            
           // Build result set to be returned as a list to R.
           return List::create(Named("date",   dv),
                               Named("datetime", dtv));
        }
    
    

Author(s)

Dominick Samperi wrote the initial versions of Rcpp (and RcppTemplate) during 2005 and 2006. Dirk Eddelbuettel made some additions, and became maintainer in 2008. Dirk Eddelbuettel and Romain Francois have been extending Rcpp since 2009.

References

Writing R Extensions, available at https://www.r-project.org.

Examples

# set up date and datetime vectors
dvec <- Sys.Date() + -2:2
dtvec <- Sys.time() + (-2:2)*0.5

# call the underlying  C++ function
result <- RcppDateExample(dvec, dtvec)

# inspect returned object
result

Examples of uses of List

Description

List is an Rcpp class that can be used to manipulate R lists.

Arguments

params

A heterogeneous list specifying method (string), tolerance (double), maxIter (int) and startDate (Date in R, RcppDate in C++).

Value

RcppListExample returns a list containing:

method

string input paramter

tolerance

double input paramter

maxIter

int input parameter

startDate

Date type with starting date

params

input parameter list (this is redundant because we returned the input parameters above)

Author(s)

Dominick Samperi wrote the initial versions of Rcpp (and RcppTemplate) during 2005 and 2006. Dirk Eddelbuettel made some additions, and became maintainer in 2008. Dirk Eddelbuettel and Romain Francois have been extending Rcpp since 2009.

References

Writing R Extensions, available at https://www.r-project.org.

Examples

# set up some value
params <- list(method='BFGS',
               tolerance=1.0e-5,
               maxIter=100,
               startDate=as.Date('2006-7-15'))

# call the underlying  C++ function
result <- RcppListExample(params)

# inspect returned object
result

Example of using Rcpp NumericMatrix

Description

The NumericMatrix class represents numeric matrices

Details

The C++ code presented in the MatrixExample.cpp file:

        #include <Rcpp.h>
        #include <cmath>
        
        // suncc needs help to disambiguate between sqrt( float ) and sqrt(double) 
        inline static double sqrt_double(double x) { return ::sqrt(x); }
        
        using namespace Rcpp; 
        
        // [[Rcpp::export]]
        List MatrixExample(const NumericMatrix & orig) {
            NumericMatrix mat(orig.nrow(), orig.ncol());	
        
            // we could query size via
            //   int n = mat.nrow(), k=mat.ncol();
            // and loop over the elements, but using the STL is so much nicer
            // so we use a STL transform() algorithm on each element
            std::transform(orig.begin(), orig.end(), mat.begin(), sqrt_double );

            return List::create(Named("result") = mat, 
                                Named("original") = orig);
        }
    
    

Author(s)

Dominick Samperi wrote the initial versions of Rcpp (and RcppTemplate) during 2005 and 2006. Dirk Eddelbuettel made some additions, and became maintainer in 2008. Dirk Eddelbuettel and Romain Francois have been extending Rcpp since 2009.

References

Writing R Extensions, available at https://www.r-project.org.

Examples

M <- matrix((1:16)^2, 4)
RcppMatrixExample(M)

Rcpp NumericVector example

Description

Example on how to use a NumericVector and manipulate it with the STL.

Details

    NumericVector orig ;                 // from R
    NumericVector vec(orig.size());	 // create a target vector of the same size
    
    // we could query size via
    //   int n = vec.size();
    // and loop over the vector, but using the STL is so much nicer
    // so we use a STL transform() algorithm on each element
    std::transform(orig.begin(), orig.end(), vec.begin(), sqrt_double );

    return List::create(Named("result") = vec, 
                        Named("original") = orig);
  

As shown in the example section, provided the seed is reset, the exact same draws can be obtained in R itself – which is important for reproducibility.

Author(s)

Dirk Eddelbuettel and Romain Francois

Examples

RcppNumericVectorExample(seq(1,9)^2)

Rcpp RNGs example

Description

Rcpp sugar provides numerous p/q/d/r functions for numerous distributions.

This example shows (in the corresponding C++ code) how to draw from three different distributions and returns a data frame.

Details

The various header file, and the Rcpp sugar vignette, provide full documentation for Rcpp sugar.

The C++ source file corresponding to the this function does the following:

        int n;  	// length passed in from R

        NumericVector rn = rnorm(n);
        NumericVector rt = rt(n, 1.0);
        NumericVector rp = rpois(n, 1.0);

        // create a new data frame to return drawns
       return DataFrame::create(Named("rnorm") = rn,
                                Named("rt")    = rt,
                                Named("rpois") = rp);
  

As shown in the example section, provided the seed is reset, the exact same draws can be obtained in R itself – which is important for reproducibility.

Author(s)

Dirk Eddelbuettel and Romain Francois

Examples

set.seed(42)
  X <- RcppRNGsExample(10L)
  set.seed(42)
  Y <- data.frame(rnorm=rnorm(10),rt=rt(10,1),rpois=rpois(10,1))
  all.equal(X,Y)

Example of using Rcpp StringVector (aka CharacterVector)

Description

The StringVector (aka CharacterVector) class represents character vectors.

Details

The C++ code presented in the StringVectorExample.cpp file:

        #include <Rcpp.h>
        using namespace Rcpp ;
        
        // [[Rcpp::export]]
        List StringVectorExample(const StringVector & orig) {
            StringVector vec(orig.size());	
        
            std::transform(orig.begin(), orig.end(), vec.begin(), 
        		   make_string_transformer(tolower));
        
            return List::create(Named("result")   = vec,
                                Named("original") = orig);
        }

    

Author(s)

Dominick Samperi wrote the initial versions of Rcpp (and RcppTemplate) during 2005 and 2006. Dirk Eddelbuettel made some additions, and became maintainer in 2008. Dirk Eddelbuettel and Romain Francois have been extending Rcpp since 2009.

References

Writing R Extensions, available at https://www.r-project.org.

Examples

RcppStringVectorExample(c("Tick", "Tack", "Tock"))