[R] Creating a sparse matrix from a file
David Winsemius
dwinsemius at comcast.net
Tue Oct 27 00:58:57 CET 2009
On Oct 26, 2009, at 5:06 AM, Pallavi Palleti wrote:
>
> Hi all,
>
> I am new to R and learning the same. I would like to create a sparse
> matrix
> from an existing file whose contents are in the format
> "rowIndex,columnIndex,value"
>
> for ex:
> 1,2,14
> 2,4,15
>
> I would like to create a sparse matrix by taking the above as input.
> However, I couldn't find an example where the data was being read
> from a
> file. I tried searching in R tutorial and also searched for the same
> in web
> but in vain. Could some one kindly help me how to give the above
> format as
> input in R to create a sparse matrix.
ex <- read.table(textConnection("1,2,14
2,4,15") , sep=",")
ex
# V1 V2 V3
#1 1 2 14
#2 2 4 15
M <- Matrix(0, 20, 20)
> M
#20 x 20 sparse Matrix of class "dsCMatrix"
[1,] . . . . . . . . . . . . . . . . . . . .
[2,] . . . . . . . . . . . . . . . . . . . .
[3,] . . . . . . . . . . . . . . . . . . . .
snip
for (i in 1:nrow(ex) ) { M[ex[i, 1], ex[i, 2] ] <- ex[i, 3] }
> M
20 x 20 sparse Matrix of class "dgCMatrix"
[1,] . 14 . . . . . . . . . . . . . . . . . .
[2,] . . . 15 . . . . . . . . . . . . . . . .
[3,] . . . . . . . . . . . . . . . . . . . .
snip
>
--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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