Transforming a Matrix with STL Algorithms

Romain Francois — written Dec 14, 2012 — source

Here we take the square root of each item of a matrix and return a new matrix with the tranformed values. We do this by using std::transform to call the sqrt function on each element of the matrix:

#include <Rcpp.h>
#include <cmath>

using namespace Rcpp;

// [[Rcpp::export]]
NumericMatrix matrixSqrt(NumericMatrix orig) {

  // allocate the matrix we will return
  NumericMatrix mat(orig.nrow(), orig.ncol());
  
  // transform it 
  std::transform(orig.begin(), orig.end(), mat.begin(), ::sqrt);
  
  // return the new matrix
  return mat;
}

Here we call the function from R:

m <- matrix(c(1,2,3, 11,12,13), nrow = 2, ncol=3)
matrixSqrt(m)

      [,1]  [,2]  [,3]
[1,] 1.000 1.732 3.464
[2,] 1.414 3.317 3.606

tags: matrix stl

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Transforming a Matrix with STL Algorithms

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