# [R] how to "multiply" list of matrices by list of vectors

arun smartpink111 at yahoo.com
Wed Feb 6 15:13:30 CET 2013

```Hi,

I got an error message with:
vlist <- apply(mm, list)

Error in match.fun(FUN) : argument "FUN" is missing, with no default
#assuming that
vlist <- apply(mm,2,list)

mapply("%*%",mlist,vlist[1:2],SIMPLIFY=FALSE)
#[]
#    [,1]
#[1,]   19
#[2,]   22
#[3,]   25
#[4,]   28
#
#[]
#    [,1]
#[1,]   67
#[2,]   74
#[3,]   81
#[4,]   88

A.K.
----- Original Message -----
From: David Romano <dromano at stanford.edu>
To: r-help at r-project.org
Cc:
Sent: Wednesday, February 6, 2013 12:50 AM
Subject: [R] how to "multiply" list of matrices by list of vectors

Hi everyone,

I'd like to be able to apply lda to each 2D matrix slice of a 3D array, and
then use the scalings to obtain the corresponding lda scores.

I can use 'apply' to get a list of the lda output for each 2D slice, and
can create a list of the resulting scalings, but I'm not sure how to
multiply them in a vectorized way.

Here's how I made a list of 2D matrices (suggestion on improving this would
be welcome, too!):

> aa <- array(1:24,c(4,2,3))
> mlist <- apply(aa,2,list)
> mlist <- lapply(mlist, unlist)
> mlist <- lapply(mlist, function(x) matrix(x,4,2))

and here's how I made a list of vectors:

> mm <- matrix(1:6,2,3)
> vlist <- apply(mm, list)
> vlist <- lapply(vlist, unlist)

Now I'd like to make the list whose i-th element is mlist[[i]]%*%vlist[[i]]
without having to loop through the indices.

Any help would be appreciated!

Thanks,
David

[[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help