Feature Request: multiple casts in to argument

[JosiahParry]

It is common that I will want to expand a multipolygon into its component linestrings. To do this I will have to cast the geometry multiple times. For example:

library(sf)
nc_path <- system.file("shape/nc.shp", package = "sf")

nc <- st_read(nc_path, quiet = TRUE) |> 
  st_geometry()

nc |> 
  st_cast("MULTILINESTRING") |> 
  st_cast("LINESTRING")
#> Geometry set for 108 features 
#> Geometry type: LINESTRING
#> Dimension:     XY
#> Bounding box:  xmin: -84.32385 ymin: 33.88199 xmax: -75.45698 ymax: 36.58965
#> Geodetic CRS:  NAD27
#> First 5 geometries:
#> LINESTRING (-81.47276 36.23436, -81.54084 36.27...
#> LINESTRING (-81.23989 36.36536, -81.24069 36.37...
#> LINESTRING (-80.45634 36.24256, -80.47639 36.25...
#> LINESTRING (-76.00897 36.3196, -76.01735 36.337...
#> LINESTRING (-76.02717 36.55672, -75.99866 36.55...

It would be a quite nice experience to be able to provide a character vector of length 2, 3, etc to specify the casts in order. For example it would be nice to be able to rewrite the above as:

nc |> 
  st_cast(c("MULTILINESTRING", "LINESTRING"))

^{Created on 2023-09-12 with reprex v2.0.2}

[dcooley]

In the absence of a native function, sfheaders::sf_cast() will do this

nc <- st_read(nc_path, quiet = TRUE) |> 
  sfheaders::sf_cast(to = "LINESTRING")