On Apr 22, 2010, at 12:24 PM, Steve Lianoglou wrote:
Hi,
On Thu, Apr 22, 2010 at 12:08 PM, karena <dr.jz...@gmail.com> wrote:
I need to create 10 matrices. say matrix 1-10.
matrix_1 is 1 by 1
matrix_2 is 2 by 2
matrix_3 is 3 by 3
.
.
.
matrix_10 is 10 by 10
I am just wondering if there are some functions in R that are
similar to the
macro variables in SAS. so I can create these 10 matrices by doing:
for (i in 1: 10) {
matrix_$i <- matrix(nrow=i, ncol=i)
}
rather thank creating these matrices one by one manually.
Anyone have any suggestions?
I believe the most idiomatic R way is to make a list of length 10:
R> mats <- lapply(1:10, function(x) matrix(0, nrow=x, ncol=x))
A somewhat similar method using Map:
mtxlist <- Map(matrix, rep(0,10), 1:10, 1:10)
names(mtxlist) <- paste("matrix", 1:10, sep="_")
mtxlist$matrix_1
mtxlist$matrix_10
Or with nested Map/mapply calls:
mtxlist <- Map(assign, paste("matx", 1:10, sep="_"), Map(matrix,
rep(0,10), 1:10, 1:10) )
And if you wanted to have all of those individual mtx_<n>'s floating
around:
mapply(assign,
paste("matx", 1:4, sep="_"),
Map(matrix, 1:4, 1:4, 1:4),
MoreArgs=list( envir=.GlobalEnv) )
Then reference them like so:
R> mats[[1]]
If you *really* want them to be in your global namespace, you have
two options:
1. You can slightly modify the `mat` list I made above with more
"variable-friendly" names and then `attach` it (or use `with`):
R> names(mats) <- paste("m", 1:10, sep="")
R> attach(mats)
R> m2
[,1] [,2]
[1,] 0 0
[2,] 0 0
2. Or you could forget the `lapply` from above use `assign` in a for
loop:
R> for (i in 1:10) {
assign(sprintf('mat%d', i), matrix(0, nrow=i, ncol=i))
}
R> mat2
[,1] [,2]
[1,] 0 0
[2,] 0 0
Other notes: using "attach" isn't really best practice -- look into
using `with`
Documentation you should read:
?lapply
?attach
?with
?assign
-steve
--
Steve Lianoglou
Graduate Student: Computational Systems Biology
| Memorial Sloan-Kettering Cancer Center
| Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact
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David Winsemius, MD
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