getting data associated with coordinates in a spatial data frame
On 13-Oct-11 20:33, Sarah Goslee wrote:
Hi, On Thu, Oct 13, 2011 at 2:05 PM, Bailey, Daniel<bailed at 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 at 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 at 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 at 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