Helping with write a function. Merging shape files?

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

 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(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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