On Tue, 9 Dec 2008, David M Warner wrote:
Greetings
I'm using R 2.8 with recent (last month) versions of the packages I need to
use at present.
I'm interested in examining hierarchical spatio-temporal patterns in a data
set. The data consist of 94 points (X, Y, UTM coordinates) at which catch
rates for a fish were recorded and there are also estimates of prey
available for these fish at the same locations. I have reason to believe
that the relationships between predators and prey varies with spatial scale
(nested processes).
To test this hypothesis, I'd like to generate subsets of the points that are
separated by distance ranges (1-50 km, 51-100 km, etc) so I can run Sncf
(package ncf) on the subsets.
I cannot find a way to do this with R code. Getting a distance matrix is
easy. Using that to help generate a series of distance-based subsets is
something I cannot figure out (without manually entering a list of all the
point pairs).
You mean subsets of _pairs_ of points, right? (If not, then say what you
meant and give an example.)
Do like this:
cv <- rnorm(20) # phony coords
dim(cv) <- c(10,2)
alldist3 <- as.matrix( dist( cv ) ) # Euclidean
cd <- cut(alldist3,c( 0, 1, 2, 4, Inf) )
sapply(levels(cd), function(x) which(array(cd == x,dim(alldist3)),arr.ind=TRUE))
$`(0,1]`
row col
[1,] 2 1
[2,] 5 1
[3,] 6 1
[4,] 9 1
[5,] 1 2
[6,] 3 2
[rest omitted]
Each element of the list contains all the pairs at the specified distance.
You'll want to clean this up to use the right distance and cutpoints and
to rid redundant pairs (2,1 vs 1,2), but you get the idea.
See
?which
?cut
?levels
?sapply
HTH,
Chuck
Any suggestions would be appreciated.
For what it's worth, I did post this question to R-sig-geo as well.
Dave Warner
David Warner
Research Fishery Biologist
USGS Great Lakes Science Center
1451 Green Road
Ann Arbor MI 48105
734.214.9392
______________________________________________
R-help@r-project.org 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.
Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:[EMAIL PROTECTED] UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
______________________________________________
R-help@r-project.org 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.
