Thanks, stack and reshape are what I needed.
Sam
Dylan Beaudette wrote:
On Friday 21 November 2008, Sam Veloz wrote:
When I tried this:
test.aov <- aov(response ~ ., data=SGDF)
It only gives the next variable in the resulting ANOVA table.
The other option you gave:
test.aov <- aov(response ~ rep1 + rep2 + rep3 + rep4 + rep5, data=SGDF)
doesn't work because it treats each "rep" as a factor, I would like each
of these rasters to be a repetition. In other words I would have an n of
5. Does this make sense?
Thanks,
Sam
In that case you need to 'stack' your data into long format. check the mailing
list for ideas. Functions of interest:
stack()
reshape()
and the 'reshape' package
Cheers,
Dylan
Roger Bivand wrote:
On Thu, 20 Nov 2008, Sam Veloz wrote:
I would like to run an anova on a set of raster variables imported
from GRASS into R but am confused about how R handles the raster data.
So if I have a model with a treatment with 2 levels, each raster is a
binary file with cells coded for each level of the treatment. I have 1
response raster layer that corresponds spatially with the treatment
layers. So let's say I have 5 rasters representing a different rep of
the treatment how would I code this in R? I started out trying this:
treatment<-readRAST6(c("rep1","rep2","rep3","rep4","rep5"),cat=TRUE)
response<-readRAST6("response",cat=FALSE)
test.aov<-aov(response~treatment)
The objects returned by readRAST6 are SpatialGridDataFrames. I think
that you may find that:
SGDF <- readRAST6(c("rep1", "rep2", "rep3", "rep4", "rep5", "response"),
cat=c(TRUE, TRUE, TRUE, TRUE, TRUE, FALSE))
test.aov <- aov(response ~ ., data=SGDF)
does the trick (the . inserts the remaining variables) - or safer:
test.aov <- aov(response ~ rep1 + rep2 + rep3 + rep4 + rep5, data=SGDF)
Untried.
By the way, do you need aov(), or would anova(lm()) do the same? I guess
the richer setting needs facilities in aov() that aren't visible here.
Hope this helps,
Roger
but I don't think this is right. Is it possible to do what I am
trying? My data is actually a bit more complicated than this but if I
can clear this up than I think I can do the rest on my own.
Thanks for your help,
Sam
--
****************************************************
Sam Veloz
Postdoctoral Researcher
Department of Environmental Science and Policy
University of California, Davis
[EMAIL PROTECTED]
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