Importing S4 functions from the Matrix package

Question

The Matrix package defines a whole bunch of S4 methods for multiplying matrices, that are dispatched by the S4 generic functions %*%, crossprod, and tcrossprod.

How do I import the "%*%" methods, for use in my own package? This piece of code fails when I run devtools::document():

#' @title my function
#'
#' @description Does magic Matrix stuff
#' @import methods
#' @importFrom Matrix "%*%" Diagonal
myfun <- function(x, y){
  x %*% Diagonal(x=y)
}

I want to make sure this function uses the sparse Matrix multiplication methods from the Matrix package if x is a sparse matrix. But when I run devtools::document() I get the following error:

Updating mypackage documentation
Loading mypackage
Error: object ‘%*%’ is not exported by 'namespace:Matrix'

Answer 1

You should use @importMethodsFrom and remove the quotes around the operator. You probably also want to export the function with @export (you may already know this but it makes the answer more complete). The following works for me without error.

#' @title my function
#'
#' @description Does magic Matrix stuff
#' @import methods
#' @importFrom Matrix Diagonal
#' @importMethodsFrom Matrix %*%
#' @export
myfun <- function(x, y){
    x %*% Diagonal(x=y)
}