From: Gabor Grothendieck <ggrothendieck_at_gmail.com>

Date: Sat 18 Feb 2006 - 13:09:15 EST

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Sat Feb 18 13:14:03 2006

Date: Sat 18 Feb 2006 - 13:09:15 EST

library(zoo)

rook2 <- function(x, i = 1) {

# test

m <- matrix(1:24, 6)

rook2(m)

On 2/17/06, Mills, Jason <Jason.Mills@afhe.ualberta.ca> wrote:

*>
*

> How do you specify matrix location a[i,j] (or a[i-1,j], etc.) in a "for"

*> loop?
**>
**> I am looking for a flexible method of indexing neighbors over a series
**> of lags (1,2,3...) and I may wish to extend this method to 3D arrays.
**>
**>
**> Example:
**>
**> Data matrix
**> > fun
**> [,1] [,2] [,3]
**> [1,] 1 5 9
**> [2,] 2 6 10
**> [3,] 3 7 11
**> [4,] 4 8 12
**>
**>
**> For each element a[i,j] in "fun", sum the 1st order (Rook's) neighbors:
**>
**> a[i-1,j]
**>
**> a[i+1,j]
**>
**> a[i,j-1]
**>
**> a[i,j+1]
**>
**> Then divide by the number of elements included as neighbors-- this
**> number depends on the location of a[i,j] in the matrix.
**>
**>
**> Insert the product of the neighbor calculation for each a[i,j] into the
**> corresponding position b[i,j] in an empty matrix with the same
**> dimensions as "fun".
**>
**>
**> For example, element [2,2] in "fun" should yield element [2,2] in a new
**> matrix equal to 24/4=6. Of course, element [1,1] in the new matrix
**> should be the product of only two numbers.
**>
**>
**> Thanks
**>
**> J. Mills
**>
**> [[alternative HTML version deleted]]
**>
**> ______________________________________________
**> R-help@stat.math.ethz.ch mailing list
**> https://stat.ethz.ch/mailman/listinfo/r-help
**> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
**>
*

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Sat Feb 18 13:14:03 2006

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