sf: st_cast – R documentation

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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 class 'MULTIPOLYGON'
st_cast(x, to, ...)

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

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

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

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

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

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

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

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

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

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

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

st_cast(x, to, ...)

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

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

## S3 method for class '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

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.

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.

Examples

# example(st_read)
nc = st_read(system.file("shape/nc.shp", package="sf"))
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")

sf

Simple Features for R

v0.9-8

GPL-2 | MIT + file LICENSE

Authors

Edzer Pebesma [aut, cre] (<https://orcid.org/0000-0001-8049-7069>), Roger Bivand [ctb] (<https://orcid.org/0000-0003-2392-6140>), Etienne Racine [ctb], Michael Sumner [ctb], Ian Cook [ctb], Tim Keitt [ctb], Robin Lovelace [ctb], Hadley Wickham [ctb], Jeroen Ooms [ctb] (<https://orcid.org/0000-0002-4035-0289>), Kirill Müller [ctb], Thomas Lin Pedersen [ctb], Dan Baston [ctb]

Initial release