R help - Aug 2010 - Multiply each depth level of an array with another vector element

Suppose

x <- array(c(1,1,1,1,2,2,2,2), dim = c(2,2,2))

y <- c(5, 10)



Now I would like to multiply x[, , 1] with y[1] and x[, , 2] with y[2].



Possible solution is a for-loop:

for (i in 1:2) {

x[, , i] * y[i]

}



Another possible solution is this construction:

as.vector(t(replicate(nrow(x) * ncol(x), y))) * x



I find that these two solutions have a relatively large computation time (on
larger arrays) and I suspect there should be solution with less computation
time. Is there a faster method to perform this calculation (thus to multiply
the depth of an array with respective vector elements)?



Best regards,

Maurits Aben

	[[alternative HTML version deleted]]

I have only achieved a half improvement.

x <- array(1:24000000*1, dim = c(200,300,400))
y <- 1:400*1
ptm <- proc.time()
z <- x*as.vector(t(replicate(dim(x)[1]*dim(x)[2], y[1:dim(x)[3]]))) 
"replicate:"
proc.time() - ptm

x <- array(1:24000000*1, dim = c(200,300,400))
y <- 1:400*1
ptm <- proc.time()
z <- x*rep(y[1:dim(x)[3]],each=dim(x)[1]*dim(x)[2])
"rep:"
proc.time() - ptm

-----
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?sweep

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.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 Maurits Aben
> Sent: Thursday, August 05, 2010 2:00 PM
> To: r-help at r-project.org
> Subject: [R] Multiply each depth level of an array with another vector
> element
> 
> Suppose
> 
> x <- array(c(1,1,1,1,2,2,2,2), dim = c(2,2,2))
> 
> y <- c(5, 10)
> 
> 
> 
> Now I would like to multiply x[, , 1] with y[1] and x[, , 2] with y[2].
> 
> 
> 
> Possible solution is a for-loop:
> 
> for (i in 1:2) {
> 
> x[, , i] * y[i]
> 
> }
> 
> 
> 
> Another possible solution is this construction:
> 
> as.vector(t(replicate(nrow(x) * ncol(x), y))) * x
> 
> 
> 
> I find that these two solutions have a relatively large computation
> time (on
> larger arrays) and I suspect there should be solution with less
> computation
> time. Is there a faster method to perform this calculation (thus to
> multiply
> the depth of an array with respective vector elements)?
> 
> 
> 
> Best regards,
> 
> Maurits Aben
> 
> 	[[alternative HTML version deleted]]
> 
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