xx <- maptools::readShapePoly(system.file("shapes/sids.shp", package="maptools")[1], IDvar="FIPSNO")
yy<-as(xx,"data.frame")
yy$newvar<-sample(letters,nrow(yy),replace=TRUE)
yy<-subset(yy,select=c("FIPS","newvar"))
newpoly<-mapmerge(xx,yy,xid="FIPS",yid="FIPS")
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