Given an object with geometries of type GEOMETRY or GEOMETRYCOLLECTION, return an object consisting only of elements of the specified type.

Source: R/collection_extract.R

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
)

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
#> Bounding box:  xmin: 5.5 ymin: -0.5 xmax: 8 ymax: 1.5
#> CRS:           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
#> Bounding box:  xmin: 5.5 ymin: -0.5 xmax: 8 ymax: 1.5
#> CRS:           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
#> Bounding box:  xmin: 3 ymin: 0 xmax: 4 ymax: 0
#> CRS:           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
#> Bounding box:  xmin: 1 ymin: 0 xmax: 1 ymax: 0
#> CRS:           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
#> Bounding box:  xmin: 5.5 ymin: -0.5 xmax: 8 ymax: 1.5
#> CRS:           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
#> Bounding box:  xmin: 3 ymin: 0 xmax: 4 ymax: 0
#> CRS:           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
#> Bounding box:  xmin: 1 ymin: 0 xmax: 1 ymax: 0
#> CRS:           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
#> Bounding box:  xmin: 5.5 ymin: -0.5 xmax: 8 ymax: 1.5
#> CRS:           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
#> Bounding box:  xmin: 5.5 ymin: -0.5 xmax: 8 ymax: 1.5
#> CRS:           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,...