sf (version 0.4-3)

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

Description

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

Usage

# 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, ...)
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)

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 unsuccesful. 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)
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))
## no closing coordinates should remain for multipoint
any(duplicated(unclass(st_cast(mpl, "MULTIPOINT"))))  ## should be 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

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))
mls <- st_cast(nc$geometry[[4]], "MULTILINESTRING")
st_sfc(cast_all(mls))
mpt <- st_cast(nc$geometry[[4]], "MULTIPOINT")
st_sfc(cast_all(mpt))
pl <- st_cast(nc$geometry[[4]], "POLYGON")
st_sfc(cast_all(pl))
ls <- st_cast(nc$geometry[[4]], "LINESTRING")
st_sfc(cast_all(ls))
pt <- st_cast(nc$geometry[[4]], "POINT")
## st_sfc(cast_all(pt))  ## Error: cannot create MULTIPOLYGON from POINT 
st_sfc(lapply(c("POINT", "MULTIPOINT"), function(x) st_cast(pt, x)))
s = st_multipoint(rbind(c(1,0)))
st_cast(s, "POINT")