R help - Dec 2011 - Moving column averaging

# need zoo to use rollapply()

# your data (I called df)
df <- structure(list(a = 1:2, b = 2:3, c = c(5L, 9L), d = c(9L, 6L), 
    e = c(1L, 5L), f = c(4, 7)), .Names = c("a", "b",
"c", "d",
"e", "f"), class = "data.frame", row.names = c(NA,
-2L))

# transpose and make a zoo object
df2 <- zoo(t(df))

#rollapply to get means and transpose back
means <- t(rollapply(df2, width=2, by=2, FUN=mean))

# adding the combined column names you requested
colnames(means) <- apply(matrix(names(df), nrow=2), 2, paste,
collapse=", ")


HTH


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On Thu, Dec 1, 2011 at 7:13 PM, B77S <bps0002 at auburn.edu>
wrote:
> # need zoo to use rollapply()
>
> # your data (I called df)
> df <- structure(list(a = 1:2, b = 2:3, c = c(5L, 9L), d = c(9L, 6L),
> ? ?e = c(1L, 5L), f = c(4, 7)), .Names = c("a", "b",
"c", "d",
> "e", "f"), class = "data.frame", row.names =
c(NA, -2L))
>
> # transpose and make a zoo object
> df2 <- zoo(t(df))
>
> #rollapply to get means and transpose back
> means <- t(rollapply(df2, width=2, by=2, FUN=mean))
>
> # adding the combined column names you requested
> colnames(means) <- apply(matrix(names(df), nrow=2), 2, paste,
collapse=", ")
>
Note that zoo's rollapply also works on plain matrices and vectors.

-- 
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com

I don't know the answer, but would suppose not.
You could test this for yourself using:
system.time()
example: 
system.time(rnorm(100000,0,1)) 


Chega wrote
> 
> This solved my problem - Thanks a lot for your help! Please allow me one
> more question: Works zoo's rollapply on a plain matrix faster than on a
> zoo object? I am asking since I wanted to apply the provided averaging
> code to a larger matrix (2500 rows x 200 cols), which is quite time
> consuming...
> 
> Thanks again!
> 
> Chega
> 
> ________________________________
> From: B77S [via R] <ml-node+s789695n4143909h3 at .nabble>
> To: Chega <chegaga@> 
> Sent: Friday, December 2, 2011 6:16 AM
> Subject: Re: Moving column averaging
> 
> 
> Sorry for that, and thanks Gabor, 
> I could have sworn that it wouldn't. 
> 
> 
> 
> Gabor Grothendieck wrote
>>On Thu, Dec 1, 2011 at 7:13 PM, B77S <[hidden email]> wrote: 
>>> # need zoo to use rollapply() 
>>> 
>>> # your data (I called df) 
>>> df <- structure(list(a = 1:2, b = 2:3, c = c(5L, 9L), d = c(9L,
6L),
>>> ? ?e = c(1L, 5L), f = c(4, 7)), .Names = c("a",
"b", "c", "d",
>>> "e", "f"), class = "data.frame",
row.names = c(NA, -2L))
>>> 
>>> # transpose and make a zoo object 
>>> df2 <- zoo(t(df)) 
>>> 
>>> #rollapply to get means and transpose back 
>>> means <- t(rollapply(df2, width=2, by=2, FUN=mean)) 
>>> 
>>> # adding the combined column names you requested 
>>> colnames(means) <- apply(matrix(names(df), nrow=2), 2, paste,
>>> collapse=", ") 
>>> 
>>
>>Note that zoo's rollapply also works on plain matrices and vectors. 
>>
>>-- 
>>Statistics & Software Consulting 
>>GKX Group, GKX Associates Inc. 
>>tel: 1-877-GKX-GROUP 
>>email: ggrothendieck at gmail.com 
>>
>>______________________________________________ 
>>[hidden email]?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. 
> 
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