[R-sig-Geo] Subsetted SpatialPolygonsDataFrame cannot writeOGR to ESRI shapefiles

[Roger Bivand]

On Wed, 2 Jun 2010, christiaan pauw wrote:

> Hallo Everybody
>
> I have been using R for a while but I am new to using R on spatial
> data. What I want to do seems fairly straightforward to me but for
> some reason it doesn't seem to work even after reading a lot of help
> files and mail threads. I want to read shapefile containing a town map
> and subset it to contain only the polygons that correspond to a
> certain field in the data frame. (i.e. selelct those houses in the
> town for which I have some other data). I have a unique stand number
> in both the dataframe and shapefile.  Then in want to merge some
> additional data from the dataframe and export back to a ESRI
> shapefile.
>
> I read the shapefiles with readOGR. The resultant object (called
> SPbluegum) is a SpatialPolygonsDataFrame
>
>> class(SPbluegum)
> [1] "SpatialPolygonsDataFrame"
> attr(,"package")
> [1] "sp"
>
> I think where things go wrong is where I try to create a new object
> that is a subset of the full town SPDF. My code is:
>
>> SPbluegumImP=SPbluegum[which(is.na(match(SPbluegum$PROPDESC,DF$Stand.Number_0))==FALSE),c(3,4,6)]
>
> This works and can be plotted. class() reveals that this too is a
> SpatialPolygonsDataFrame but it cannot be written with writeOGR. This
> puzzles me since the error message reads:"unknown data type"
>
>> writeOGR(SPbluegumImp, dsn=paste(outdir,sep=""), layer="BluegumImpMap", driver="ESRI Shapefile")
> Error in writeOGR(SPbluegumImp, dsn = paste(outdir, sep = ""), layer =
> "BluegumImpMap",  :
>  unknown data type
>
> Please show me where I go wrong

Please always report the version number of the package involved (usually 
with sessionInfo() output). In this case, the error message formatting was 
improved last year, so your rgdal is seriously out-of-date. Update first, 
then if the error re-occurs, you'll know which variable in the data slot 
of the object cannot be exported. More likely, it will be cast to another 
representation in the updated rgdal.

Roger

>
> best regards
> Christiaan
>
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no