Simple way to subset SpatialPolygonsDataFrame (i.e. delete polygons) by attribute in R
mapping, r, r-maptools, spatial
Solution
looks like you're overwriting the data, but not removing the polygons. If you want to cut down the dataset including both data and polygons, try e.g.
world.map <- world.map[world.map$AREA > 30000,]
plot(world.map)
[[Edit 19 April, 2016]] That solution used to work, but @Bonnie reports otherwise for a newer R version (though perhaps the data has changed too?): `world.map <- world.map[world.map@data$AREA > 30000, ]` Upvote @Bonnie's answer if that helped.
Problem
I would like simply delete some polygons from a SpatialPolygonsDataFrame object based on corresponding attribute values in the @data data frame so that I can plot a simplified/subsetted shapefile. So far I haven't found a way to do this. For example, let's say I want to delete all polygons from this world shapefile that have an area of less than 30000. How would I go about doing this? Or, similarly, how can I delete Antartica? ``` require(maptools) getinfo.shape("TM_WORLD_BORDERS_SIMPL-0.3.shp") # Shapefile type: Polygon, (5), # of Shapes: 246 world.map <- readShapeSpatial("TM_WORLD_BORDERS_SIMPL-0.3.shp") class(world.map) # [1] "SpatialPolygonsDataFrame" # attr(,"package") # [1] "sp" head(world.map@data) # FIPS ISO2 ISO3 UN NAME AREA POP2005 REGION SUBREGION LON LAT # 0 AC AG ATG 28 Antigua and Barbuda 44 83039 19 29 -61.783 17.078 # 1 AG DZ DZA 12 Algeria 238174 32854159 2 15 2.632 28.163 # 2 AJ AZ AZE 31 Azerbaijan 8260 8352021 142 145 47.395 40.430 # 3 AL AL ALB 8 Albania 2740 3153731 150 39 20.068 41.143 # 4 AM AM ARM 51 Armenia 2820 3017661 142 145 44.563 40.534 # 5 AO AO AGO 24 Angola 124670 16095214 2 17 17.544 -12.296 ``` If I do something like this, the plot does not reflect any changes. ``` world.map@data = world.map@data[world.map@data$AREA > 30000,] plot(world.map) ``` same result if I do this: ``` world.map@data = world.map@data[world.map@data$NAME != "Antarctica",] plot(world.map) ``` Any help is appreciated!