I believe Peter figured it out on his own off list. Here was my solution
using rgdal:


library(rgdal)

# Shapefile's full path is '/home/matt/LynchingHotSpots.
shp' on my computer
# If you had your file at 'C:\data\LynchingHotSpots.shp' you would change
#            shpFolder to "C:/data"   and   shpLayer stays as
"LynchingHotSpots"
shpFolder <- "/home/matt"
shpLayer <- "LynchingHotSpots"
spdf <- readOGR(shpFolder,shpLayer,p4s="+proj=longlat +datum=NAD27")
spdf     # SpatialPolygonsDataFrame

# Pick out the states of interest
statesWanted <-
c("Mississippi","Louisiana","Alabama","Tennessee","Georgia","South
Carolina","North Carolina","Kentucky")
subSpdf <- spdf[spdf$STATE_NAME %in% statesWanted,]

# Original vs. Subsetted
dim(spdf)                    # 3141 by 16
dim(subSpdf)                 # 733 by 16
spplot(spdf,"Lynchings")     # original
spplot(subSpdf,"Lynchings")  # subsetted


# Create pdf of results
pdf("LynchingResults.pdf")
spplot(subSpdf,"Lynchings")
dev.off()

Matt Beard
Purdue University


On Mon, May 31, 2010 at 12:18 AM, Don MacQueen <macq@llnl.gov> wrote:

>
> Supposing that your data object is named "mydata", try following this
> example:
>
>  mydata[ , STATE_NAME %in% c('name1','name2','name17') ]
>
> replacing my fake state names with the ones you want.
>
> If you have another variable that identifies the subset you want, use it
> instead of STATE_NAME.
>
> This example assumes you data is in a SpatialPolygonsDataFrame.
>
> You haven't really provided enough information for more specific
> suggestions.
>
> -Don
>

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