R help - Sep 2011 - Multiplying a list of matrices with a vector

Hi all!

I have a list of matrices and I want to multiply the ith element of the list
with the ith element of a another vector. That is,
> LL <- list(A=diag(3),B=diag(3),C=diag(3))
> vec <- 1:3
> for(i in 1:3)
+ {
+   LL[[i]] <- LL[[i]]*vec[i]
+ }
> LL
$A
     [,1] [,2] [,3]
[1,]    1    0    0
[2,]    0    1    0
[3,]    0    0    1

$B
     [,1] [,2] [,3]
[1,]    2    0    0
[2,]    0    2    0
[3,]    0    0    2

$C
     [,1] [,2] [,3]
[1,]    3    0    0
[2,]    0    3    0
[3,]    0    0    3

Is there another (more efficient) way of doing this without using loops? I found
an older entry in this list with a similar problem, where the list elements were
always multiplied with the same number, e.g., lapply(LL, function(x) x*3) and I
was looking for something similar.

Best,
Franco

Untested:

mapply('*', LL, vec)

Those should be backticks but I can't type them on my phone

Michael

On Sep 28, 2011, at 6:04 PM, "Mendolia, Franco" <fmendolia at
mcw.edu> wrote:
> Hi all!
> 
> I have a list of matrices and I want to multiply the ith element of the
list with the ith element of a another vector. That is,
> 
>> LL <- list(A=diag(3),B=diag(3),C=diag(3))
>> vec <- 1:3
>> for(i in 1:3)
> + {
> +   LL[[i]] <- LL[[i]]*vec[i]
> + }
>> LL
> $A
>     [,1] [,2] [,3]
> [1,]    1    0    0
> [2,]    0    1    0
> [3,]    0    0    1
> 
> $B
>     [,1] [,2] [,3]
> [1,]    2    0    0
> [2,]    0    2    0
> [3,]    0    0    2
> 
> $C
>     [,1] [,2] [,3]
> [1,]    3    0    0
> [2,]    0    3    0
> [3,]    0    0    3
> 
> Is there another (more efficient) way of doing this without using loops? I
found an older entry in this list with a similar problem, where the list
elements were always multiplied with the same number, e.g., lapply(LL,
function(x) x*3) and I was looking for something similar.
> 
> Best,
> Franco
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.