subset SpatialPolygonsDataFrame using negative index?

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
No, the negative index doesn't work, I'll try to commit a fix to sp. In 
fact, I'd rather do:

nm <- readShapePoly("co35_d00.shp", proj4string=CRS("+proj=longlat"))
nm1 <- unionSpatialPolygons(nm, nm$COUNTY)
df <- as(nm, "data.frame")[-13,]
row.names(df) <- df$COUNTY
nm2 <- SpatialPolygonsDataFrame(nm1, df)

which makes a multipolygon for Sandoval and drops the attributes for the 
second member polygon.

Hope this helps,

Roger
# 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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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

subset SpatialPolygonsDataFrame using negative index?

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