Thank you so much Matt. I will try this code with my data. I like to
merge all shape files of a county (SSURGO polygons) and want to
create a single shape file for a state. I did it before for 15 states
of NE-region of USA. I used ArcGIS. I do not like to work with ArcGIS.
I now it is not possible to do this kind of analysis in R under Windows
O/S due to memory issue. Once I able to run this code correctly, then I
will try this code in my new linux system (32 GB memory )
Thanks again
Zia
Matt Beard wrote:
Zia,
The error you received was 'invalid class "SpatialPolygons" object:
non-unique Polygons ID slot values'.
Renaming the Polygons IDs so that they are unique should fix your problem.
The following code along with some test shapefiles I used are attached.
library(rgdal)
setwd("C:/test")
# obtain shapefiles in current directory
files <- list.files(pattern = "shp")
# get polygons from first file
data.first <- readOGR(files[1], gsub(".shp","",files[1]))
polygons <- slot(data.first, "polygons")
# add polygons from remaining files
for (i in 2:length(files)) {
data.temp <- readOGR(files[i], gsub(".shp","",files[i]))
polygons <- c(slot(data.temp, "polygons"),polygons)
}
# rename IDs of Polygons
for (i in 1:length(polygons)) {
slot(polygons[[i]], "ID") <- paste(i)
}
# ain't that spatial
spatialPolygons <- SpatialPolygons(polygons)
spdf <- SpatialPolygonsDataFrame(spatialPolygons,
data.frame(fakeData=1:length(polygons)))
# output combined results
plot(spatialPolygons)
writeOGR(spdf, dsn="C:/test/combined.shp", layer="combined",
driver="ESRI Shapefile")
# end of code
My test shapefiles had very different attribute tables, so I didn't
bother combining the data tables.
However, the code above should at least show you that your method can
work.
I found it interesting that when I combined the polygons in the
opposite order:
polygons <- c(polygons,slot(data.temp, "polygons"))
the SoutheasternStates polygons completely covered up the Florida
polygons in QGis, but
the Florida polygons showed up when plotting in R:
plot(spatialPolygons)
Does the R 'plot' function order the polygons before displaying them?
Is it possible to view the code
for a function like plot(SpatialPolygons)?
Matt
On Wed, Jan 20, 2010 at 4:14 PM, Zia Ahmed <z...@cornell.edu
<mailto:z...@cornell.edu>> wrote:
Thanks! I am trying to write a function to merge or combine
several shape files.
First I try to use following function when all shape files in one
folder. It showed error.
setwd("E:/Zia/SURRGO_Data/SSURGO_RAW_DATA/Test1")
library(rgdal)
## obtain shapefile names in current directory
fs <- list.files(pattern = "shp")
## read the first one
d <- readOGR(fs[1], gsub(".shp", "", fs[1]))
for (i in 2:length(fs)) {
d.tmp <- readOGR(fs[i], gsub(".shp", "", fs[i]))
}
d <- rbind(d, d.tmp)
> d <- rbind(d, d.tmp)
Error in validObject(.Object) :
invalid class "SpatialPolygons" object: non-unique Polygons ID
slot values
Then I am trying to use following code, but it did not work. it
_created a empty layer. _I think I did something wrong. Any idea,
# Code for similar file name (shape.shp)
setwd("E:/Zia/SURRGO_Data/SSURGO_RAW_DATA/Testf")
library(rgdal)
files <- list.files(pattern = "shp") # get all the names in the
directory
files <- files[file.info <http://file.info>(files)$isdir] # only
keep the directories
layer<- file('layer.shp') # output file
for (Dir in files){
input <- readOGR(file.path(Dir, "shape.shp"))
rbind(input, layer)
}
close(layer)
I have a situations like all shape files are different names
(like...001.shp, ...003.shp, ....005.shp so on ) and were saved
in different folders (like fn001, fn003, fn005....... If someone
helps me to write correct code for solving this it will be great.
Zia
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