sf_cast: sf cast

In sfheaders: Converts Between R Objects and Simple Feature Objects

sf cast

Description

convert the input sf to a different geometry

Usage

sf_cast(sf, to, close = TRUE, list_columns = NULL)

Arguments

sf	object to convert
to	the geometry to convert to.
close	logical indicating if polygons should be closed
list_columns	vector of column names or indexes. List columns are columns of data where there is a value corresponding to each coordinate in the geometry (sfc). List columns get cast with the geometries.

Examples

df <- data.frame(
 id1 = c(1,1,1,1,1,1,1,1,2,2,2,2)
 , id2 = c(1,1,1,1,2,2,2,2,1,1,1,1)
 , x = c(0,0,1,1,1,1,2,2,3,4,4,3)
 , y = c(0,1,1,0,1,2,2,1,3,3,4,4)
)

pt <- sf_point(obj = df, x = "x", y = "y", z = "id1")
mpt <- sf_multipoint(obj = df, x = "x", y = "y", multipoint_id = "id1")
ls <- sf_linestring(obj = df, x = "x", y = "y", linestring_id = "id1")
mls <- sf_multilinestring(obj = df, x = "x", y = "y", multilinestring_id = "id1")
p <- sf_polygon(
  obj = df
  , x = "x"
  , y = "y"
  , polygon_id = "id1"
  , linestring_id = "id2"
  , close = FALSE
  )
mp <- sf_multipolygon(
  obj = df
  , x = "x"
  , y = "y"
  , multipolygon_id = "id1"
  , linestring_id = "id2"
  , close = FALSE
  )

sf_cast( pt, "LINESTRING" )
sf_cast( mpt, "POLYGON" )
sf_cast( ls, "POINT" )
sf_cast( mls, "MULTIPOLYGON" )
sf_cast( p, "POINT" )
sf_cast( mp, "LINESTRING" )


## List Columns

df <- data.frame(
 id1 = c(1,1,1,1,1,1,1,1,2,2,2,2)
 , id2 = c(1,1,1,1,2,2,2,2,1,1,1,1)
 , x = c(0,0,1,1,1,1,2,2,3,4,4,3)
 , y = c(0,1,1,0,1,2,2,1,3,3,4,4)
)

## Add a column where each value is an attribute of each coordinate
df$val <- letters[1:nrow(df)]

## Make a multipolygon, and specify `val` as a list_column
mp <- sf_multipolygon(
  obj = df
  , x = "x"
  , y = "y"
  , multipolygon_id = "id1"
  , linestring_id = "id2"
  , list_column = "val"
  , keep = TRUE
  , close = FALSE
  )

## The 'val' attributes follow the same structure as the geometry column
## So each 'val' corresponds to a single coordinate in the geometry
str( mp )

## specifying `list_columns = "val"` when casting will retain the association
## between the 'val' attribute and each coordinate.
res <- sf_cast( mp, "LINESTRING", list_columns = "val" )

## The 'val' attribute still follows the same structure as the geometry column
str( res )

sfheaders documentation built on July 9, 2023, 7:41 p.m.