Extract parts of one type from geometry collections

Gathers the points, lines, or polygons of each geometry into a single multipoint, multilinestring, or multipolygon. ga_collection_extract() flattens nested collections and multi part members in order.

Usage

ga_collection_extract(geometry, geometry_type = "POLYGON")

Arguments

geometry

a GeoArrow geometry array

geometry_type

one of "POLYGON", "LINESTRING", or "POINT"

Value

a GeoArrow multipolygon, multilinestring, or multipoint array of the same length as geometry

Details

Unlike sf::st_collection_extract(), ga_collection_extract() keeps one row per input row. It returns a null for a geometry with no parts of geometry_type, such as a linestring when you ask for polygons, and for a null geometry.

See also

Other cast: ga_as_point(), ga_cast_geometry(), ga_downcast_geometry(), ga_explode(), ga_flatten(), ga_from_wkb()

Examples

gc <- sf::st_geometrycollection(list(
  sf::st_point(c(5, 5)),
  sf::st_polygon(list(rbind(c(0, 0), c(1, 0), c(1, 1), c(0, 0))))
))
g <- geoarrow::as_geoarrow_array(sf::st_sfc(gc, sf::st_point(c(0, 0))))

# the point has no polygons, so its row is null
as.vector(ga_geometry_type(ga_collection_extract(g, "POLYGON")))
#> [1] "MULTIPOLYGON" NA