Given an object with geometries of type GEOMETRY or GEOMETRYCOLLECTION, return an object consisting only of elements of the specified type.
Similar to ST_CollectionExtract in PostGIS. If there are no sub-geometries of the specified type, an empty geometry is returned.
st_collection_extract( x, type = c("POLYGON", "POINT", "LINESTRING"), warn = FALSE ) ## S3 method for class 'sfg' st_collection_extract( x, type = c("POLYGON", "POINT", "LINESTRING"), warn = FALSE ) ## S3 method for class 'sfc' st_collection_extract( x, type = c("POLYGON", "POINT", "LINESTRING"), warn = FALSE ) ## S3 method for class 'sf' st_collection_extract( x, type = c("POLYGON", "POINT", "LINESTRING"), warn = FALSE )
x |
an object of class |
type |
character; one of "POLYGON", "POINT", "LINESTRING" |
warn |
logical; if |
An object having the same class as x
, with geometries
consisting only of elements of the specified type.
For sfg
objects, an sfg
object is returned if there is only
one geometry of the specified type, otherwise the geometries are combined
into an sfc
object of the relevant type. If any subgeometries in the
input are MULTI, then all of the subgeometries in the output will be MULTI.
pt <- st_point(c(1, 0)) ls <- st_linestring(matrix(c(4, 3, 0, 0), ncol = 2)) poly1 <- st_polygon(list(matrix(c(5.5, 7, 7, 6, 5.5, 0, 0, -0.5, -0.5, 0), ncol = 2))) poly2 <- st_polygon(list(matrix(c(6.6, 8, 8, 7, 6.6, 1, 1, 1.5, 1.5, 1), ncol = 2))) multipoly <- st_multipolygon(list(poly1, poly2)) i <- st_geometrycollection(list(pt, ls, poly1, poly2)) j <- st_geometrycollection(list(pt, ls, poly1, poly2, multipoly)) st_collection_extract(i, "POLYGON") st_collection_extract(i, "POINT") st_collection_extract(i, "LINESTRING") ## A GEOMETRYCOLLECTION aa <- rbind(st_sf(a=1, geom = st_sfc(i)), st_sf(a=2, geom = st_sfc(j))) ## With sf objects st_collection_extract(aa, "POLYGON") st_collection_extract(aa, "LINESTRING") st_collection_extract(aa, "POINT") ## With sfc objects st_collection_extract(st_geometry(aa), "POLYGON") st_collection_extract(st_geometry(aa), "LINESTRING") st_collection_extract(st_geometry(aa), "POINT") ## A GEOMETRY of single types bb <- rbind( st_sf(a = 1, geom = st_sfc(pt)), st_sf(a = 2, geom = st_sfc(ls)), st_sf(a = 3, geom = st_sfc(poly1)), st_sf(a = 4, geom = st_sfc(multipoly)) ) st_collection_extract(bb, "POLYGON") ## A GEOMETRY of mixed single types and GEOMETRYCOLLECTIONS cc <- rbind(aa, bb) st_collection_extract(cc, "POLYGON")
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