R help - Aug 2013 - Vectorized version of colMeans/rowMeans for higher dimension arrays?

For matrices, colMeans/rowMeans are quick, vectorized functions.  But
say I have a higher dimensional array:

moo <- array(runif(400*9*3),dim=c(400,9,3))

And I want to get the mean along the 2nd dimension.  I can, of course,
use apply:

moo1 <- apply(moo,c(1,3),mean)

But this is not a vectorized operation (so it doesn't execute as
quickly).  How would one vectorize this operation (if possible)?  Is
there an array equivalent of colMeans/rowMeans?

--j

-- 
Jonathan A. Greenberg, PhD
Assistant Professor
Global Environmental Analysis and Remote Sensing (GEARS) Laboratory
Department of Geography and Geographic Information Science
University of Illinois at Urbana-Champaign
607 South Mathews Avenue, MC 150
Urbana, IL 61801
Phone: 217-300-1924
http://www.geog.illinois.edu/~jgrn/
AIM: jgrn307, MSN: jgrn307 at hotmail.com, Gchat: jgrn307, Skype: jgrn3007

Hi,
You could try:
res<-colMeans(aperm(moo,c(2,1,3)))
resOld<-apply(moo,c(1,3),mean)
?identical(res,resOld)
#[1] TRUE

#Speed:
set.seed(285)
moo1<- array(runif(1400*9*15),dim=c(1400,9,15))

system.time({res1<- colMeans(aperm(moo1,c(2,1,3)))})
?#user? system elapsed 
?# 0.004?? 0.000?? 0.002 

system.time({res2<- apply(moo1,c(1,3),mean)})
?# user? system elapsed 
?# 0.180?? 0.000?? 0.178 
identical(res1,res2)
#[1] TRUE


A.K.



----- Original Message -----
From: Jonathan Greenberg <jgrn at illinois.edu>
To: r-help <r-help at r-project.org>
Cc: 
Sent: Thursday, August 29, 2013 6:36 PM
Subject: [R] Vectorized version of colMeans/rowMeans for higher dimension
arrays?

For matrices, colMeans/rowMeans are quick, vectorized functions.? But
say I have a higher dimensional array:

moo <- array(runif(400*9*3),dim=c(400,9,3))

And I want to get the mean along the 2nd dimension.? I can, of course,
use apply:

moo1 <- apply(moo,c(1,3),mean)

But this is not a vectorized operation (so it doesn't execute as
quickly).? How would one vectorize this operation (if possible)?? Is
there an array equivalent of colMeans/rowMeans?

--j

-- 
Jonathan A. Greenberg, PhD
Assistant Professor
Global Environmental Analysis and Remote Sensing (GEARS) Laboratory
Department of Geography and Geographic Information Science
University of Illinois at Urbana-Champaign
607 South Mathews Avenue, MC 150
Urbana, IL 61801
Phone: 217-300-1924
http://www.geog.illinois.edu/~jgrn/
AIM: jgrn307, MSN: jgrn307 at hotmail.com, Gchat: jgrn307, Skype: jgrn3007

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