rcpp_apply_generator: Rcpp Apply Generator
In Kmisc: Kevin Miscellaneous

Use this function as a generator for your own apply functions; that is, functions you would like to apply over rows or columns of a matrix.

rcpp_apply_generator(fun, includes = NULL, depends = NULL, inline = TRUE,
  returnType = "double", name = NULL, file = NULL, additional = NULL)

Rcpp_apply_generator(fun, includes = NULL, depends = NULL, inline = TRUE,
  returnType = "double", name = NULL, file = NULL, additional = NULL)

`fun`	A character string defining the C++ function. It must be in terms of a variable `x`, and it must return a `double`. `x` is a reference to the current row/column being iterated over.
`includes`	Other C++ libraries to include. For example, to include boost/math.hpp, you could pass c("<boost/math.hpp>"). Rcpp is included by default, unless RcppArmadillo is included as well (since Rcpp is included as part of the RcppArmadillo include)
`depends`	Other libraries to link to. Linking is done through Rcpp attributes.
`inline`	boolean; mark this function as inline? This may or may not increase execution speed.
`returnType`	The return type of your function; must be a scalar that is `wrap`pable by Rcpp. Currently, the supported choices are `double`, `int`, and `bool`.
`name`	An internal name for the function.
`file`	A location to output the file. Defaults to a temporary file as generated by `tempfile()`.
`additional`	Other C++ code you want to include; e.g. helper functions. This code will be inserted as-is above the code in `fun`.

## Not run: 
x <- matrix(1:16, nrow=4)
cvApply <- rcpp_apply_generator("return mean(x) / sd(x);")
squaredSumApply <- rcpp_apply_generator("
  double out = 0;
  for( int i=0; i < x.size(); i++ ) {
    out += x[i];
  }
  out = out*out;
  return out;
  ")
cvApply(x, 2)
apply(x, 2, mean) / apply(x, 2, sd)
if( require(microbenchmark) ) {
 f <- function(x) { mean(x) / sd(x) }
 microbenchmark( cvApply(x, 2), apply(x, 2, f) )
}
## example with bool
anyBig <- rcpp_apply_generator( returnType="bool", '
  return is_true( any( x > 10 ) );
  ')
anyBig(x, 2)
anyBig(x, 1)
## example with boost's gcd. silly but demonstrative.
## intended to be applied to matrices with 2 rows and n columns
gcdApply <- rcpp_apply_generator( returnType="int",
  includes="<boost/math/common_factor.hpp>",
  fun='
  return boost::math::gcd( (int)x[0], (int)x[1] );
  ')
M <- matrix( c(4, 6, 20, 25, 10, 100), nrow=2 )
gcdApply(M, 2)

## End(Not run)