R help - Feb 2013 - 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]]

Try:

n <- length(mlist)
result <- lapply(1:n,function(i,m,v){m[[i]]%*%v[[i]]},m=mlist,v=vlist)

These days the use of lapply is unlikely to be much, if at all, faster than
the use of a for loop.

     cheers,

         Rolf Turner

On 02/06/2013 06:50 PM, David Romano wrote:
> 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!

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]
#[1,] ? 19
#[2,] ? 22
#[3,] ? 25
#[4,] ? 28
#
#[[2]]
?# ? ?[,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
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Thanks Rolf and Arun!   -David

On Wed, Feb 6, 2013 at 6:13 AM, arun <smartpink111@yahoo.com> wrote:
> 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]
> #[1,]   19
> #[2,]   22
> #[3,]   25
> #[4,]   28
> #
> #[[2]]
>  #    [,1]
> #[1,]   67
> #[2,]   74
> #[3,]   81
> #[4,]   88
>
> A.K.
> ----- Original Message -----
> From: David Romano <dromano@stanford.edu>
> To: r-help@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@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.
>
>
	[[alternative HTML version deleted]]