[GRASS-stats] help coding an anova using raster data

[Sam Veloz]

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


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
sdveloz at ucdavis.edu