[R] Get the indices of non-zero entries of a sparse matrix in R

[David Winsemius]

On Jul 6, 2010, at 3:46 PM, G FANG wrote:

> Hi,
>
> I am trying to get the indices of non-zero entries of a sparse  
> matrix in R
>
>     s    r d
> 1 1089 3772 1
> 2 1109  190 1
> 3 1109 2460 1
> 4 1109 3071 1
> 5 1109 3618 1
> 6 1109   38 1
>
> I found that the following can create a sparse matrix,
>
> library(Matrix)
> Y <- sparseMatrix(s,r,x=d)
>
> but have not idea and did not find online how to convert a sparse
> matrix back to three columns efficiently, i.e. get the indices of
> non-zero entries of a sparse matrix.
>
> In matlab, the find function can do this efficiently, I am wondering
> is there a similar one in R?
Yes there is, and it was reasonably easy to find with the help systems  
starting from the Matrix help page.

?sparseMatrix

summary(Y)

-- 
David Winsemius, MD
West Hartford, CT