sf (version 0.9-8)

# 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, ...)# 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

When converting a GEOMETRYCOLLECTION to COMPOUNDCURVE, MULTISURFACE or CURVEPOLYGON, the user is responsible for the validity of the resulting object: no checks are being carried out by the software.

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

```# NOT RUN {
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")
# }
```