Cast geometry to another type: either simplify, or cast explicitly

# S3 method for MULTIPOLYGON
st_cast(x, to, ...)

# S3 method for MULTILINESTRING
st_cast(x, to, ...)

# S3 method for MULTIPOINT
st_cast(x, to, ...)

# S3 method for POLYGON
st_cast(x, to, ...)

# S3 method for LINESTRING
st_cast(x, to, ...)

# S3 method for POINT
st_cast(x, to, ...)

# S3 method for GEOMETRYCOLLECTION
st_cast(x, to, ...)

# S3 method for CIRCULARSTRING
st_cast(x, to, ...)

# S3 method for MULTISURFACE
st_cast(x, to, ...)

# S3 method for COMPOUNDCURVE
st_cast(x, to, ...)

# S3 method for MULTICURVE
st_cast(x, to, ...)

# S3 method for CURVE
st_cast(x, to, ...)

st_cast(x, to, ...)

# S3 method for sfc
st_cast(x, to, ..., ids = seq_along(x), group_or_split = TRUE)

# S3 method for sf
st_cast(x, to, ..., warn = TRUE, do_split = TRUE)

# S3 method for sfc_CIRCULARSTRING
st_cast(x, to, ...)

Arguments

x

object of class sfg, sfc or sf

to

character; target type, if missing, simplification is tried; when x is of type sfg (i.e., a single geometry) then to needs to be specified.

...

ignored

ids

integer vector, denoting how geometries should be grouped (default: no grouping)

group_or_split

logical; if TRUE, group or split geometries; if FALSE, carry out a 1-1 per-geometry conversion.

warn

logical; if TRUE, warn if attributes are assigned to sub-geometries

do_split

logical; if TRUE, allow splitting of geometries in sub-geometries

Value

object of class to if successful, or unmodified object if unsuccessful. If information gets lost while type casting, a warning is raised.

In case to is missing, st_cast.sfc will coerce combinations of "POINT" and "MULTIPOINT", "LINESTRING" and "MULTILINESTRING", "POLYGON" and "MULTIPOLYGON" into their "MULTI..." form, or in case all geometries are "GEOMETRYCOLLECTION" will return a list of all the contents of the "GEOMETRYCOLLECTION" objects, or else do nothing. In case to is specified, if to is "GEOMETRY", geometries are not converted, else, st_cast will try to coerce all elements into to; ids may be specified to group e.g. "POINT" objects into a "MULTIPOINT", if not specified no grouping takes place. If e.g. a "sfc_MULTIPOINT" is cast to a "sfc_POINT", the objects are split, so no information gets lost, unless group_or_split is FALSE.

Details

the st_cast method for sf objects can only split geometries, e.g. cast MULTIPOINT into multiple POINT features. In case of splitting, attributes are repeated and a warning is issued when non-constant attributes are assigned to sub-geometries. To merge feature geometries and attribute values, use aggregate or summarise.

Examples

# example(st_read) nc = st_read(system.file("shape/nc.shp", package="sf"))
#> Reading layer `nc' from data source `/tmp/RtmpnRHNNJ/temp_libpath1381650468c/sf/shape/nc.shp' using driver `ESRI Shapefile' #> Simple feature collection with 100 features and 14 fields #> geometry type: MULTIPOLYGON #> dimension: XY #> bbox: xmin: -84.32385 ymin: 33.88199 xmax: -75.45698 ymax: 36.58965 #> epsg (SRID): 4267 #> proj4string: +proj=longlat +datum=NAD27 +no_defs
mpl <- nc$geometry[[4]] #st_cast(x) ## error 'argument "to" is missing, with no default' cast_all <- function(xg) { lapply(c("MULTIPOLYGON", "MULTILINESTRING", "MULTIPOINT", "POLYGON", "LINESTRING", "POINT"), function(x) st_cast(xg, x)) } st_sfc(cast_all(mpl))
#> Warning: polygon from first part only
#> Warning: line from first ring only
#> Warning: point from first coordinate only
#> Geometry set for 6 features #> geometry type: GEOMETRY #> dimension: XY #> bbox: xmin: -76.33025 ymin: 36.07282 xmax: -75.77316 ymax: 36.55716 #> epsg (SRID): NA #> proj4string: NA #> First 5 geometries:
#> MULTIPOLYGON (((-76.00897 36.3196, -76.01735 36...
#> MULTILINESTRING ((-76.00897 36.3196, -76.01735 ...
#> MULTIPOINT ((-76.00897 36.3196), (-76.01735 36....
#> POLYGON ((-76.00897 36.3196, -76.01735 36.33773...
#> LINESTRING (-76.00897 36.3196, -76.01735 36.337...
## no closing coordinates should remain for multipoint any(duplicated(unclass(st_cast(mpl, "MULTIPOINT")))) ## should be FALSE
#> [1] FALSE
## number of duplicated coordinates in the linestrings should equal the number of polygon rings ## (... in this case, won't always be true) sum(duplicated(do.call(rbind, unclass(st_cast(mpl, "MULTILINESTRING")))) ) == sum(unlist(lapply(mpl, length))) ## should be TRUE
#> [1] TRUE
p1 <- structure(c(0, 1, 3, 2, 1, 0, 0, 0, 2, 4, 4, 0), .Dim = c(6L, 2L)) p2 <- structure(c(1, 1, 2, 1, 1, 2, 2, 1), .Dim = c(4L, 2L)) st_polygon(list(p1, p2))
#> POLYGON ((0 0, 1 0, 3 2, 2 4, 1 4, 0 0), (1 1, 1 2, 2 2, 1 1))
mls <- st_cast(nc$geometry[[4]], "MULTILINESTRING") st_sfc(cast_all(mls))
#> Warning: keeping first linestring only
#> Warning: keeping first coordinate only
#> Geometry set for 6 features #> geometry type: GEOMETRY #> dimension: XY #> bbox: xmin: -76.33025 ymin: 36.07282 xmax: -75.77316 ymax: 36.55716 #> epsg (SRID): NA #> proj4string: NA #> First 5 geometries:
#> MULTIPOLYGON (((-76.00897 36.3196, -76.01735 36...
#> MULTILINESTRING ((-76.00897 36.3196, -76.01735 ...
#> MULTIPOINT ((-76.00897 36.3196), (-76.01735 36....
#> POLYGON ((-76.00897 36.3196, -76.01735 36.33773...
#> LINESTRING (-76.00897 36.3196, -76.01735 36.337...
mpt <- st_cast(nc$geometry[[4]], "MULTIPOINT") st_sfc(cast_all(mpt))
#> Warning: point from first coordinate only
#> Geometry set for 6 features #> geometry type: GEOMETRY #> dimension: XY #> bbox: xmin: -76.33025 ymin: 36.07282 xmax: -75.77316 ymax: 36.55716 #> epsg (SRID): NA #> proj4string: NA #> First 5 geometries:
#> MULTIPOLYGON (((-76.00897 36.3196, -76.01735 36...
#> MULTILINESTRING ((-76.00897 36.3196, -76.01735 ...
#> MULTIPOINT ((-76.00897 36.3196), (-76.01735 36....
#> POLYGON ((-76.00897 36.3196, -76.01735 36.33773...
#> LINESTRING (-76.00897 36.3196, -76.01735 36.337...
pl <- st_cast(nc$geometry[[4]], "POLYGON")
#> Warning: polygon from first part only
st_sfc(cast_all(pl))
#> Warning: point from first coordinate only
#> Geometry set for 6 features #> geometry type: GEOMETRY #> dimension: XY #> bbox: xmin: -76.33025 ymin: 36.07282 xmax: -75.79885 ymax: 36.55716 #> epsg (SRID): NA #> proj4string: NA #> First 5 geometries:
#> MULTIPOLYGON (((-76.00897 36.3196, -76.01735 36...
#> MULTILINESTRING ((-76.00897 36.3196, -76.01735 ...
#> MULTIPOINT ((-76.00897 36.3196), (-76.01735 36....
#> POLYGON ((-76.00897 36.3196, -76.01735 36.33773...
#> LINESTRING (-76.00897 36.3196, -76.01735 36.337...
ls <- st_cast(nc$geometry[[4]], "LINESTRING")
#> Warning: line from first ring only
st_sfc(cast_all(ls))
#> Warning: point from first coordinate only
#> Geometry set for 6 features #> geometry type: GEOMETRY #> dimension: XY #> bbox: xmin: -76.33025 ymin: 36.07282 xmax: -75.79885 ymax: 36.55716 #> epsg (SRID): NA #> proj4string: NA #> First 5 geometries:
#> MULTIPOLYGON (((-76.00897 36.3196, -76.01735 36...
#> MULTILINESTRING ((-76.00897 36.3196, -76.01735 ...
#> MULTIPOINT ((-76.00897 36.3196), (-76.01735 36....
#> POLYGON ((-76.00897 36.3196, -76.01735 36.33773...
#> LINESTRING (-76.00897 36.3196, -76.01735 36.337...
pt <- st_cast(nc$geometry[[4]], "POINT")
#> Warning: point from first coordinate only
## st_sfc(cast_all(pt)) ## Error: cannot create MULTIPOLYGON from POINT st_sfc(lapply(c("POINT", "MULTIPOINT"), function(x) st_cast(pt, x)))
#> Geometry set for 2 features #> geometry type: GEOMETRY #> dimension: XY #> bbox: xmin: -76.00897 ymin: 36.3196 xmax: -76.00897 ymax: 36.3196 #> epsg (SRID): NA #> proj4string: NA
#> POINT (-76.00897 36.3196)
#> MULTIPOINT ((-76.00897 36.3196))
s = st_multipoint(rbind(c(1,0))) st_cast(s, "POINT")
#> Warning: point from first coordinate only
#> POINT (1 0)