On 13-Oct-11 20:33, Sarah Goslee wrote:
Hi,
On Thu, Oct 13, 2011 at 2:05 PM, Bailey, Daniel<bai...@spu.edu> wrote:
Thank you Sarah. I tried your suggestion, and if I coerce it into a normal data.frame, that method works. But if you've
already made the data into a SpatialPixelsDataFrame and run coordinates (both from the package "sp") so that
the columns "x" and "y" become a single column "coordinates" with the format (0, 17) for
x and y, how do you then call or manipulate data at a specific location?
The following:
e[e$coordinates==(0,17),]
Doesn't work.
They "don't become a single column" but rather a single matrix with
two columns, and (0, 17) isn't the correct way to specify a vector.
You can identify particular coordinates using the form I offered
earlier, and then use that to subset the data slot of your SGPF.
Using built-in data:
library(sp)
data(meuse.grid)
m = SpatialPixelsDataFrame(points = meuse.grid[c("x", "y")], data = meuse.grid)
m@data[coordinates(m)[,"x"] == 181100& coordinates(m)[,"y"] == 333660,]
There ought to be a more elegant way to match coordinates (other than
the do.call() and paste() approach), but I'm not sure what it is.
Not sure if it is nicer, but another possibility is:
data(meuse.grid)
coordinates(meuse.grid) = ~x+y
meuse.grid@data[which(duplicated(rbind(c(181100, 333660),
coordinates(meuse.grid))))-1,] = factor(c(1,2,3,4,1))
To avoid numerical problems, you can also find the data of the location
closest to the point you are interested in:
meuse.grid@data[which.min(spDistsN1(meuse.grid, c(181100, 333660))),] =
factor(c(1,1,1,1,1))
For questions about spatial data you can also use the mailing-list
r-sig-geo.
Cheers,
Jon
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