Patrick, thank you. This works. I can't believe I have wasted several hours
in front of computer  for something this easy! :))

2011/6/21 Patrick Breheny [via R] <
ml-node+3614530-1847060061-246803@n4.nabble.com>

> On 06/21/2011 09:48 AM, davefrederick wrote:
> > Hi, I have a 500x 53380 sparse matrix and I am trying to dichotomize it.
> > Under sna package I have found event2dichot yet it doesnt recognize
> sparse
> > matrix and requires adjacency matrix or array. I tried to run a simple
> loop
> > code
> >
> > for (i in 1:500)
> > for (j in 1:53380)
> > if (matrix[i,j]>0) matrix[i,j]=1
>
> The code you are running does not require a loop:
>
>  > A <- cbind(c(1,0),c(0,2))
>  > A
>       [,1] [,2]
> [1,]    1    0
> [2,]    0    2
>  > A[A>0] <- 1
>  > A
>       [,1] [,2]
> [1,]    1    0
> [2,]    0    1
>
> However, for large sparse matrices, this and other operations will be
> faster if the matrix is explicitly stored as a sparse matrix, as
> implemented in the 'Matrix' package.
>
> --
> Patrick Breheny
> Assistant Professor
> Department of Biostatistics
> Department of Statistics
> University of Kentucky
>
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