[R] On-demand importing of a package

[Gabor Grothendieck]

On Tue, Nov 22, 2011 at 3:16 PM, Gábor Csárdi <csardi at rmki.kfki.hu> wrote:
> Dear All,
>
> in some functions of my package, I use the Matrix S4 class, as defined
> in the Matrix package.
>
> I don't want to depend on Matrix, however, because my package is
> perfectly fine without Matrix, most of the functionality does not need
> Matrix. Matrix is so included in the 'Suggests' line.
>
> I load Matrix via require(), from the functions that really need it.
> This mostly works fine, but I have an issue now that I cannot sort
> out.
>
> If I define a function like this in my package:
>
> f <- function() {
>  require(Matrix)
>  res <- sparseMatrix(dims=c(5, 5), i=1:5, j=1:5, x=1:5)
>  y <- rowSums(res)
>  res / y
> }
>
> then calling it from the R prompt I get
> Error in rowSums(res) : 'x' must be an array of at least two dimensions
>
> which basically means that the rowSums() in the base package is
> called, not the S4 generic in the Matrix package. Why is that?
> Is there any way to work around this problem, without depending on Matrix?
>
> I am doing this on R 2.14.0, x86_64-apple-darwin9.8.0.
>

Try adding these three lines to the package:

rowSums <- function(x, na.rm = FALSE, dims = 1L) UseMethod("rowSums")
rowSums.dgCMatrix <- Matrix:::rowSums
rowSums.default <- base::rowSums

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