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 sfg
st_collection_extract(
  x,
  type = c("POLYGON", "POINT", "LINESTRING"),
  warn = FALSE
)

# S3 method for sfc
st_collection_extract(
  x,
  type = c("POLYGON", "POINT", "LINESTRING"),
  warn = FALSE
)

# S3 method for sf
st_collection_extract(
  x,
  type = c("POLYGON", "POINT", "LINESTRING"),
  warn = FALSE
)

Arguments

x

an object of class sf, sfc or sfg that has mixed geometry (GEOMETRY or GEOMETRYCOLLECTION).

type

character; one of "POLYGON", "POINT", "LINESTRING"

warn

logical; if TRUE, warn if attributes are assigned to sub-geometries when casting (see st_cast)

Value

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.

Examples

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")
#> Geometry set for 2 features #> geometry type: POLYGON #> dimension: XY #> bbox: xmin: 5.5 ymin: -0.5 xmax: 8 ymax: 1.5 #> epsg (SRID): NA #> proj4string: NA
#> POLYGON ((5.5 0, 7 0, 7 -0.5, 6 -0.5, 5.5 0))
#> POLYGON ((6.6 1, 8 1, 8 1.5, 7 1.5, 6.6 1))
st_collection_extract(i, "POINT")
#> POINT (1 0)
st_collection_extract(i, "LINESTRING")
#> LINESTRING (4 0, 3 0)
## 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")
#> Simple feature collection with 5 features and 1 field #> geometry type: MULTIPOLYGON #> dimension: XY #> bbox: xmin: 5.5 ymin: -0.5 xmax: 8 ymax: 1.5 #> epsg (SRID): NA #> proj4string: NA #> a geom #> 1.2 1 MULTIPOLYGON (((5.5 0, 7 0,... #> 1.3 1 MULTIPOLYGON (((6.6 1, 8 1,... #> 2.2 2 MULTIPOLYGON (((5.5 0, 7 0,... #> 2.3 2 MULTIPOLYGON (((6.6 1, 8 1,... #> 2.4 2 MULTIPOLYGON (((5.5 0, 7 0,...
st_collection_extract(aa, "LINESTRING")
#> Simple feature collection with 2 features and 1 field #> geometry type: LINESTRING #> dimension: XY #> bbox: xmin: 3 ymin: 0 xmax: 4 ymax: 0 #> epsg (SRID): NA #> proj4string: NA #> a geom #> 1.1 1 LINESTRING (4 0, 3 0) #> 2.1 2 LINESTRING (4 0, 3 0)
st_collection_extract(aa, "POINT")
#> Simple feature collection with 2 features and 1 field #> geometry type: POINT #> dimension: XY #> bbox: xmin: 1 ymin: 0 xmax: 1 ymax: 0 #> epsg (SRID): NA #> proj4string: NA #> a geom #> 1 1 POINT (1 0) #> 2 2 POINT (1 0)
## With sfc objects st_collection_extract(st_geometry(aa), "POLYGON")
#> Geometry set for 5 features #> geometry type: MULTIPOLYGON #> dimension: XY #> bbox: xmin: 5.5 ymin: -0.5 xmax: 8 ymax: 1.5 #> epsg (SRID): NA #> proj4string: NA
#> MULTIPOLYGON (((5.5 0, 7 0, 7 -0.5, 6 -0.5, 5.5...
#> MULTIPOLYGON (((6.6 1, 8 1, 8 1.5, 7 1.5, 6.6 1)))
#> MULTIPOLYGON (((5.5 0, 7 0, 7 -0.5, 6 -0.5, 5.5...
#> MULTIPOLYGON (((6.6 1, 8 1, 8 1.5, 7 1.5, 6.6 1)))
#> MULTIPOLYGON (((5.5 0, 7 0, 7 -0.5, 6 -0.5, 5.5...
st_collection_extract(st_geometry(aa), "LINESTRING")
#> Geometry set for 2 features #> geometry type: LINESTRING #> dimension: XY #> bbox: xmin: 3 ymin: 0 xmax: 4 ymax: 0 #> epsg (SRID): NA #> proj4string: NA
#> LINESTRING (4 0, 3 0)
#> LINESTRING (4 0, 3 0)
st_collection_extract(st_geometry(aa), "POINT")
#> Geometry set for 2 features #> geometry type: POINT #> dimension: XY #> bbox: xmin: 1 ymin: 0 xmax: 1 ymax: 0 #> epsg (SRID): NA #> proj4string: NA
#> POINT (1 0)
#> POINT (1 0)
## 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")
#> Simple feature collection with 2 features and 1 field #> geometry type: MULTIPOLYGON #> dimension: XY #> bbox: xmin: 5.5 ymin: -0.5 xmax: 8 ymax: 1.5 #> epsg (SRID): NA #> proj4string: NA #> a geom #> 3 3 MULTIPOLYGON (((5.5 0, 7 0,... #> 4 4 MULTIPOLYGON (((5.5 0, 7 0,...
## A GEOMETRY of mixed single types and GEOMETRYCOLLECTIONS cc <- rbind(aa, bb) st_collection_extract(cc, "POLYGON")
#> Simple feature collection with 7 features and 1 field #> geometry type: MULTIPOLYGON #> dimension: XY #> bbox: xmin: 5.5 ymin: -0.5 xmax: 8 ymax: 1.5 #> epsg (SRID): NA #> proj4string: NA #> a geom #> 1.2 1 MULTIPOLYGON (((5.5 0, 7 0,... #> 1.3 1 MULTIPOLYGON (((6.6 1, 8 1,... #> 2.2 2 MULTIPOLYGON (((5.5 0, 7 0,... #> 2.3 2 MULTIPOLYGON (((6.6 1, 8 1,... #> 2.4 2 MULTIPOLYGON (((5.5 0, 7 0,... #> 5 3 MULTIPOLYGON (((5.5 0, 7 0,... #> 6 4 MULTIPOLYGON (((5.5 0, 7 0,...