[R-sig-Geo] combining polygons from shapefiles...

[Sean O'Riordain]

Good afternoon,

I've been making good progress in the last few weeks thanks to this
list, along with Roger and Adrians' books and some great geo-packages.

I'm trying to combine some shapefiles...

library(maptools)
CA <- readShapePoly('ca.shp')
LA <- readShapePoly('la.shp')

Now I want to combine these two into a bigger object...

I've searched the books and the internet and I've tried a number of
things... including...

> class(LA)
[1] "SpatialPolygonsDataFrame"
attr(,"package")
[1] "sp"
> class(CA)
[1] "SpatialPolygonsDataFrame"
attr(,"package")
[1] "sp"
>
>     S1 <- unionSpatialPolygons(CA, LA)
Loading required package: gpclib
General Polygon Clipper Library for R (version 1.4-4)
        Type 'class ? gpc.poly' for help

Error in unionSpatialPolygons(CA, LA) : input lengths differ
>
>
> S1 <- spRbind(CA, LA)
Error in spRbind(as(obj, "SpatialPolygons"), as(x, "SpatialPolygons")) :
  non-unique polygon IDs
>

Any ideas please?

Thanks in advance!
Sean