Re: [R] Question on Reduce + rollmean

Muhammad Rahiz Thu, 07 Jan 2010 09:32:40 -0800

Dear Gabor & Henrique,

Thanks for your suggestions on the above problem. The following is more 
traditional and unfanciful but it works. Suitable for a prodige like myself...


m <- matrix(1:3,3,3)

x1 <- list(m, m+1, m+2, m+3, m+4)

out <- list()
for (i in 1:4){
t[[i]] <- Reduce("+", x1[c(i:i+1)])
}

Muhammad

Muhammad Rahiz  |  Doctoral Student in Regional Climate Modeling                
                        
Climate Research Laboratory, School of Geography & the Environment  
Oxford University Centre for the Environment

South Parks Road, Oxford, OX1 3QY, United KingdomTel: +44 (0)1865-285194 Mobile: +44 (0)7854-625974

Email: [email protected]






Gabor Grothendieck wrote:

Here is a variation which also uses head and tail:

mapply(function(x, y) (x + y)/2, tail(x, -1), head(x, -1), SIMPLIFY = FALSE)


On Mon, Jan 4, 2010 at 12:37 PM, Henrique Dallazuanna <[email protected]> wrote:

For this example try this:

lapply(lapply(list('head', 'tail'), do.call, list(x, n = -1)),
function(x)Reduce('+', x)/2)


On Mon, Jan 4, 2010 at 1:54 PM, Muhammad Rahiz
<[email protected]> wrote:

Thanks Gabor,

It works alright. But is there alternative ways to perform rollmean apart
from permutating the data?
Possibly combining the Reduce and rollmean functions?

The easiest but traditional way is

(x[[1]]+x[[2]]) / 2
(x[[2]]+x[[3]]) / 2

Muhammad Rahiz  |  Doctoral Student in Regional Climate Modeling

Climate Research Laboratory, School of Geography & the Environment
Oxford University Centre for the Environment
South Parks Road, Oxford, OX1 3QY, United Kingdom Tel: +44 (0)1865-285194
 Mobile: +44 (0)7854-625974
Email: [email protected]






Gabor Grothendieck wrote:

Try apply:

library(zoo) # rollmean

# test data
m <- matrix(1:3, 3, 3)
x <- list(m, m+3, m+6)

# convert to array
a <- array(unlist(x), c(3, 3, 3)); a

# apply rollmean and permute to desired form
aa <- apply(a, 1:2, rollmean, k = 2)
aperm(aa, c(2, 3, 1))

The last line outputs:

aperm(aa, c(2, 3, 1))

, , 1

    [,1] [,2] [,3]
[1,]  2.5  2.5  2.5
[2,]  3.5  3.5  3.5
[3,]  4.5  4.5  4.5

, , 2

    [,1] [,2] [,3]
[1,]  5.5  5.5  5.5
[2,]  6.5  6.5  6.5
[3,]  7.5  7.5  7.5


On Sat, Jan 2, 2010 at 10:00 AM, Muhammad Rahiz
<[email protected]> wrote:

Let me rephrase;

Given x as

[[1]]
 V1 V2 V3
[1,]  1  1  1
[2,]  2  2  2
[3,]  3  3  3

[[2]]
 V1 V2 V3
[1,]  4  4  4
[2,]  5  5  5
[3,]  6  6  6

[[3]]
 V1 V2 V3
[1,]  7  7  7
[2,]  8  8  8
[3,]  9  9  9

I'd like to calculate the moving average (interval = 2) i.e.

( x[[1]] + x[[2]] ) / 2
( x[[2]] + x[[3]] ) / 2
... and so on.

The desired output will return

2.5 2.5 2.5
3.5 3.5 3.5
4.5 4.5 4.5

5.5 5.5 5.5
6.5 6.5 6.5
7.5 7.5 7.5




Muhammad Rahiz  |  Doctoral Student in Regional Climate Modeling
Climate Research Laboratory, School of Geography & the Environment
Oxford University Centre for the Environment, University of Oxford
South Parks Road, Oxford, OX1 3QY, United Kingdom
Tel: +44 (0)1865-285194  Mobile: +44 (0)7854-625974
Email: [email protected]



milton ruser wrote:

Dear M.Rahiz,

Unfortunatelly I can't reproduce your example.
PLEASE do read the posting guide

http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html>

bests

milton
On Sat, Jan 2, 2010 at 9:26 AM, Muhammad Rahiz
<[email protected]<mailto:[email protected]>>
wrote:
Hello useRs,

I'd like to perform a moving average on the dataset, xx. I've tried
combining the functions Reduce and rollmean but it didn't work.

r <- function(n) rollmean(n, 2) # where 2 = averaging interval
output < - Reduce("r", x)

Error in f(init, x[[i]]) : unused argument(s) (x[[i]])

Is there anything wrong with the code in the first place?

where

[[1]]
 V1 V2 V3
[1,]  1  1  1
[2,]  2  2  2
[3,]  3  3  3

[[2]]
 V1 V2 V3
[1,]  4  4  4
[2,]  5  5  5
[3,]  6  6  6

[[3]]
 V1 V2 V3
[1,]  7  7  7
[2,]  8  8  8
[3,]  9  9  9

The moving average is to be performed on

1,4,7 = (1+4)/2 , (4+7)/2
2,5,8 = ..
3,6,9 = ..

Thanks

Muhammad

--
Muhammad Rahiz  |  Doctoral Student in Regional Climate Modeling
Climate Research Laboratory, School of Geography & the Environment
Oxford University Centre for the Environment, University of Oxford
South Parks Road, Oxford, OX1 3QY, United Kingdom
Tel: +44 (0)1865-285194  Mobile: +44 (0)7854-625974
Email: [email protected]<mailto:[email protected]>

______________________________________________
[email protected]<mailto:[email protected]> mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide

http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html>
and provide commented, minimal, self-contained, reproducible code.

______________________________________________
[email protected] 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.

______________________________________________
[email protected] 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-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

______________________________________________
[email protected] 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.


______________________________________________
[email protected] 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.

Re: [R] Question on Reduce + rollmean

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