R help - Nov 2007 - Multiply each column of array by vector component

Hi,

I've got an array, say with i,jth entry = A_ij, and a vector, say with jth
entry= v_j. I would like to multiply each column of the array by the
corresponding vector component, i,e. find the array with i,jth entry

A_ij * v_j

This seems so basic but I can't figure out how to do it without a loop.
Any suggestions?

Michal.

?sweep

b

On Nov 15, 2007, at 12:50 PM, M.T.Charemza at warwick.ac.uk wrote:
> Hi,
>
> I've got an array, say with i,jth entry = A_ij, and a vector, say with 
> jth
> entry= v_j. I would like to multiply each column of the array by the
> corresponding vector component, i,e. find the array with i,jth entry
>
> A_ij * v_j
>
> This seems so basic but I can't figure out how to do it without a loop.
> Any suggestions?
>
> Michal.
>
> ______________________________________________
> 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.

On Nov 15, 2007 12:50 PM,  <M.T.Charemza at warwick.ac.uk>
wrote:
> Hi,
>
> I've got an array, say with i,jth entry = A_ij, and a vector, say with
jth
> entry= v_j. I would like to multiply each column of the array by the
> corresponding vector component, i,e. find the array with i,jth entry
>
> A_ij * v_j
>
> This seems so basic but I can't figure out how to do it without a loop.
> Any suggestions?
>
Here are 4 ways:


A <- matrix(1:6, 3)
v <- 10:11

A %*% diag(v)

A * rep(1, nrow(A)) %o% v

t(t(A) * v)

A * replace(A, TRUE, v[col(A)])

?sweep

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at intermountainmail.org
(801) 408-8111
 
 
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of 
> M.T.Charemza at warwick.ac.uk
> Sent: Thursday, November 15, 2007 10:50 AM
> To: r-help at r-project.org
> Subject: [R] Multiply each column of array by vector component
> 
> Hi,
> 
> I've got an array, say with i,jth entry = A_ij, and a vector, 
> say with jth entry= v_j. I would like to multiply each column 
> of the array by the corresponding vector component, i,e. find 
> the array with i,jth entry
> 
> A_ij * v_j
> 
> This seems so basic but I can't figure out how to do it 
> without a loop.
> Any suggestions?
> 
> Michal.
> 
> ______________________________________________
> 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.
>

If i understand your question, you can do:

x <- matrix(1:10, 2)
y <- sample(10,5)
apply(x, 1, function(.x)mapply(y, .x, FUN="*"))


On 15/11/2007, M.T.Charemza at warwick.ac.uk <M.T.Charemza at
warwick.ac.uk> wrote:
> Hi,
>
> I've got an array, say with i,jth entry = A_ij, and a vector, say with
jth
> entry= v_j. I would like to multiply each column of the array by the
> corresponding vector component, i,e. find the array with i,jth entry
>
> A_ij * v_j
>
> This seems so basic but I can't figure out how to do it without a loop.
> Any suggestions?
>
> Michal.
>
> ______________________________________________
> 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.
>

-- 
Henrique Dallazuanna
Curitiba-Paran?-Brasil
25? 25' 40" S 49? 16' 22" O

On Thu, 2007-11-15 at 17:50 +0000, M.T.Charemza at warwick.ac.uk
wrote:
> Hi,
> 
> I've got an array, say with i,jth entry = A_ij, and a vector, say with
jth
> entry= v_j. I would like to multiply each column of the array by the
> corresponding vector component, i,e. find the array with i,jth entry
> 
> A_ij * v_j
> 
> This seems so basic but I can't figure out how to do it without a loop.
> Any suggestions?
> 
> Michal.
If I understand you correctly:

  t(t(A) * v)


set.seed(1)

A <- matrix(sample(20), ncol = 2)
v <- c(5, 2)
> A
      [,1] [,2]
 [1,]    6    3
 [2,]    8    2
 [3,]   11   20
 [4,]   16   10
 [5,]    4    5
 [6,]   14    7
 [7,]   15   12
 [8,]    9   17
 [9,]   19   18
[10,]    1   13

> t(t(A) * v)
      [,1] [,2]
 [1,]   30    6
 [2,]   40    4
 [3,]   55   40
 [4,]   80   20
 [5,]   20   10
 [6,]   70   14
 [7,]   75   24
 [8,]   45   34
 [9,]   95   36
[10,]    5   26

HTH,

Marc Schwartz