xx <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1],
IDvar="FIPSNO", proj4string=CRS("+proj=longlat +ellps=clrk66"))
summary(xx)
xx$FIPSNO
xx1 <- xx[xx$CNTY_ID < 1982,]
xx2 <- xx[xx$CNTY_ID >= 1982,]
xx3 <- spRbind(xx2, xx1)
summary(xx3)
xx3$FIPSNO
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