[R-sig-Geo] subset SpatialPolygonsDataFrame using negative index?
stubben
stubben at lanl.gov
Wed Oct 21 22:33:52 CEST 2009
I loaded a county map of New Mexico from census.gov
nm <- readShapePoly("co35_d00.shp", proj4string=CRS("+proj=longlat"))
This map has 34 counties because Sandoval county occurs twice (which
is funny since there is one missing in the maps database). I'd like
to remove the extra polygon which is very small, but a negative index
doesn't work
# remove 13th row
n<-which(nm2 at data$AREA<0.0005)
n
[1] 13
# using negative index
nm1<-nm[-n,]
# only one county displayed on map
plot(nm1)
## because plotOrder =1?
str(nm1,2)
Formal class 'SpatialPolygonsDataFrame' [package "sp"] with 5 slots
..@ data :'data.frame': 33 obs. of 9 variables:
..@ polygons :List of 33
..@ plotOrder : int 1
..@ bbox : num [1:2, 1:2] -109.1 31.3 -103 37
.. ..- attr(*, "dimnames")=List of 2
..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots
## this works, but I'm just wondering why the negative index doesn't
work? Am I doing something wrong?
nm2<-nm[c(1:12,14:34),]
plot(nm2)
str(nm2,2)
Formal class 'SpatialPolygonsDataFrame' [package "sp"] with 5 slots
..@ data :'data.frame': 33 obs. of 9 variables:
..@ polygons :List of 33
..@ plotOrder : int [1:33] 22 23 28 2 25 3 9 12 24 14 ...
..@ bbox : num [1:2, 1:2] -109.1 31.3 -103 37
.. ..- attr(*, "dimnames")=List of 2
..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots
Thanks,
Chris Stubben
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