matrix to vector
Ian Coe wrote:
Hi, Is there a way to convert a matrix into a vector representing all permutations of values and column/row headings with native R functions? I did this with 2 nested for loops and it took about 25 minutes to run on a ~700x700 matrix. I'm assuming there must be a smarter way to do this with R's vector commands, but being new to R, I'm having trouble making it work.
> cbind(expand.grid(rownames(x),colnames(x)),as.vector(x))
Var1 Var2 as.vector(x)
1 d a 1
2 e a 2
3 f a 3
4 d b 4
5 e b 5
6 f b 6
7 d c 7
8 e c 8
9 f c 9
> x <- matrix(rnorm(700*700),700)
> rownames(x) <- paste("R",1:700)
> colnames(x) <- paste("C",1:700)
> system.time(foo <-
cbind(expand.grid(rownames(x),colnames(x)),as.vector(x)))
user system elapsed
1.082 0.107 1.193
Thanks,
Ian
[a] [b] [c]
[d] 1 4 7
[e] 2 5 8
[f] 3 6 9
a d 1
a e 2
a f 3
b d 4
b e 5
b f 6
c d 7
c e 8
c f 9
Ian Coe
Connective Capital Management, LLC
385 Homer Ave.
Palo Alto, CA 94301
(650) 321-4826 ext. 03
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