Simple way to subset SpatialPolygonsDataFrame (i.e. delete polygons) by attribute in R

Question

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 simplifi

Answer 1

As a second pointer: this does not work for shapefiles with "holes" in the shapes, because it is subsetting by index.