st_rbindlist: Convert a list of sf objects to a single sf object

In a-benini/sfhelpers: Helper Functions for Wrapping Simple Features-Related Routines

Convert a list of sf objects to a single sf object

Description

A fast alternative to do.call(rbind, <list_of_sf>)

Usage

st_rbindlist(l, ..., geometry_name = NULL)

Arguments

l	list of objects of the class sf
...	arguments of the function rbindlist except l
geometry_name	a single character string giving a user-defined name to the returned active list-column with simple feature geometries. If unspecified / by default (NULL), the geometry column name is inherited from the first sf object listed in the input.

Details

st_rbindlist() is basically a wrapper for sf::st_as_sf(data.table::rbindlist(<list_of_sf>)), which is a fast alternative to do.call(rbind, <list_of_sf>). It comes with some properties which rbind has, but rbindlist misses:

• checks if all sf objects included in the input share the same CRS

• returns a sf object with a correct bbox (more information on how to handle this rbindlist issue can be found here).

• allows binding sf objects with different geometry types

Remarks about matching geometry columns of input sf objects:

• If the attribute columns are identically named, but differ by position within each sf object, set use.names = TRUE and fill = TRUE.

• If the geometry and/or attribute columns are differently named, but have same position within every sf object, set use.names = FALSE.

• In any case the active geometry columns of the listed sf-objects are matched due to the identical internal naming of these columns.

Value

a sf object

See Also

vignette("rbindlist_issues")

Examples

library(sf)

# a set of geometries to work with
nc <- st_read(system.file("gpkg/nc.gpkg", package = "sf"), quiet = TRUE)

# proof of concept with a list of sf-objects having identically named and
# positioned attribute and geometry columns:
list_of_sf <- lapply(1:nrow(nc), function(x) nc[x, ])
nc_new <- st_rbindlist(list_of_sf)
all.equal(nc, nc_new)

# a list of sf-objects having ...
l <- lapply(
  1:3,
  function(x){data.frame(nc[x, 1:3]) %>% setNames(., c(paste0(names(.), "_", x))) %>% st_sf()}
)
# ... differently named, but identically positioned geometry & attribute columns
sapply(l, names) %>% t()
# by setting use.name = FALSE such a list of sf-objects is easy to stack:
st_rbindlist(l, use.name = FALSE)

# from which listed element / sf-object do the stacked features originate?
l <- list(A = nc[1, 1:3], B = NULL, C = nc[2:3, 1:3])
st_rbindlist(l, idcol = "ID")

# list of sf-objects with identically named, but differently positioned
# geometry and attribute columns (the latter might not be included in
# each listed sf-object) ...
l <- list(nc[1, NULL], nc[2, 1], nc[3, 2:3])
# ... requires use.name = TRUE and fill = TRUE:
st_rbindlist(l, use.name = TRUE, fill = TRUE, idcol = TRUE)

# list of sf-objects with differently named and positioned geometry columns,
# and (if existing) identically named attribute columns ...
l <- lapply(
  seq_along(l),
  function(x) st_set_geometry(l[[x]], paste0("geom_", x))
  )
sapply(l, attr, "sf_column") # geometry column names of listed sf-objects

# ... can be handled also by setting use.name = TRUE and fill = TRUE:
st_rbindlist(l, use.name = TRUE, fill = TRUE, idcol = TRUE)
# this works because st_rbindlist() internally renames all active geometry columns identically!

# note: as shown above the name of the returned geometry column ...
# ... is inherited by default from the first listed sf-object. The user ...
# ... can set an alternative geometry column name:
st_rbindlist(l, use.name = TRUE, fill = TRUE, idcol = TRUE,
            geometry_name = "geom_named_by_user")

a-benini/sfhelpers documentation built on Aug. 28, 2024, 3:30 a.m.