[R] A question on operation on list
Tony Plate
tplate at acm.org
Wed Jul 22 21:39:59 CEST 2009
Here's one way:
> set.seed(1)
> x1 <- lapply(1:5, function(i) rnorm(2))
> x2 <- lapply(x1, function(x) outer(x, x))
> Reduce("+", x2, 0)
[,1] [,2]
[1,] 1.768406 -1.534413
[2,] -1.534413 3.890200
>
and another way using the abind package:
> library(abind)
> dim(abind(along=0, x2))
[1] 5 2 2
> colSums(abind(along=0, x2))
[,1] [,2]
[1,] 1.768406 -1.534413
[2,] -1.534413 3.890200
>
-- Tony Plate
megh wrote:
> Hi,
> I have created a list object like that :
> x = vector("list")
> for (i in 1:5) x[[i]] = rnorm(2)
> x
>
> Now I want to do two things :
> 1. for each i, I want to do following matrix calculation : t(x[[i]]) %*%
> x[[i]] i.e. for each i, I want to get a 2x2 matrix
> 2. Next I want to get x[[1]] + x[[2]] +....
>
> I did following : res=vector("list"); res = sapply(x, function(i) t(x[[i]])
> %*% x[[i]])
> However above syntax is not giving desired result. Any suggestion please?
>
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