On Thu, Oct 13, 2011 at 2:44 PM, Bailey, Daniel <bai...@spu.edu> wrote:
> Michael, that's half of the problem solved (whew!!). Now how do I change the
> data at that location?
You assign it a new value, just as for any assignment. Using the
example from my previous email:
> data(meuse.grid)
> m = SpatialPixelsDataFrame(points = meuse.grid[c("x", "y")], data =
> meuse.grid)
>
> m@data[coordinates(m)[,"x"] == 181100 & coordinates(m)[,"y"] == 333660,]
x y part.a part.b dist soil ffreq
5 181100 333660 1 0 0 1 1
>
> m@data[coordinates(m)[,"x"] == 181100 & coordinates(m)[,"y"] == 333660,
> "soil"] <- 5
>
> m@data[coordinates(m)[,"x"] == 181100 & coordinates(m)[,"y"] == 333660,]
x y part.a part.b dist soil ffreq
5 181100 333660 1 0 0 5 1
>
> This is not an intuitive way to manipulate data.
That's not what it's *for*. SGDFs are for storing and working with
spatial data, where all the components are needed for the spatial
reference. If you need to manipulate a lot of things, you're better
off doing it before you construct the SGDF, or you can cheat by
extracting the data slot, working with it, then reassigning it as a
single unit.
mydata <- m@data
# do stuff
m@data <- mydata
You might also benefit from reading "Applied Spatial Data Analysis
with R" by Bivand et al.
Sarah
--
Sarah Goslee
http://www.functionaldiversity.org
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