On Fri, 21 Nov 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?
No, it doesn't. Each raster given the current region in GRASS has an equal
number of cells, so all of the rasters you move to R have the same size
and resolution. You asked the rep* to be treated as factors - did you do
summary(SGDF) to see what is inside? The term "a repetition" isn' clear at
all - are these plot masks or what?
Roger
Thanks,
Sam
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
--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: [EMAIL PROTECTED]
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