[R-sig-Geo] subselection of Polygons

[Stéphane Dray]

Sorry,
the line which does not work is :

xxx <- xx[-which(xx$SID74 < 2),]



Stéphane Dray wrote:
> Hello list,
>
> I have a question concerning the [ operator for SPDF. Consider the 
> following example :
>
> library(maptools)
> xx <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1], IDvar="FIPSNO", proj4string=CRS("+proj=longlat +ellps=clrk66"))
> plot(xx, border="blue", axes=TRUE, las=1)
> text(getSpPPolygonsLabptSlots(xx), labels=getSpPPolygonsIDSlots(xx), cex=0.6)
> as(xx, "data.frame")[1:5, 1:6]
> xxx <- xx[xx$SID74 < 2,]
>
> The last line is equivalent to :
>
> xxx <- xx[which(xx$SID74 < 2),]
>
> I supposed that I can easily have the inverse selection by using '-' but 
> it does not work :
>
> xxx <- xx[which(xx$SID74 < 2),]
>
> returns the following error message :
>
> Erreur dans validObject(.Object) : invalid class "SpatialPolygons" 
> object: length mismatch
>
> I do not understand what is the problem (sp 0.9-8, R 2.4.0).
>
> Thanks,
>
>   


-- 
Stéphane DRAY (dray at biomserv.univ-lyon1.fr )
Laboratoire BBE-CNRS-UMR-5558, Univ. C. Bernard - Lyon I
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