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Count geometry components

Source: R/ddbs_queries.R
ddbs_get_npoints.Rd

Functions to count the number of points, sub-geometries or interior rings in a geometry

Usage

ddbs_get_npoints(
  x,
  new_column = "npoints",
  conn = NULL,
  name = NULL,
  mode = NULL,
  overwrite = FALSE,
  quiet = FALSE
)

ddbs_get_ngeometries(
  x,
  new_column = "ngeometries",
  conn = NULL,
  name = NULL,
  mode = NULL,
  overwrite = FALSE,
  quiet = FALSE
)

ddbs_get_ninterior_rings(
  x,
  new_column = "ninterior_rings",
  conn = NULL,
  name = NULL,
  mode = NULL,
  overwrite = FALSE,
  quiet = FALSE
)

Arguments

x

Input spatial data. Can be:

  • A duckspatial_df object (lazy spatial data frame via dbplyr)

  • An sf object

  • A tbl_lazy from dbplyr

  • A character string naming a table/view in conn

Data is returned from this object.

new_column

Name of the new column to create on the input data. Ignored with mode = "sf".

conn

A connection object to a DuckDB database. If NULL, the function runs on a temporary DuckDB database.

name

A character string of length one specifying the name of the table, or a character string of length two specifying the schema and table names. If NULL (the default), no table is written and the result is returned as a duckspatial_df or sf object, depending on mode

mode

Character. Controls the return type. Options:

  • "duckspatial" (default): Lazy spatial data frame backed by dbplyr/DuckDB

  • "sf": Eagerly collected sf object (uses memory)

Can be set globally via ddbs_options(mode = "...") or per-function via this argument. Per-function overrides global setting.

overwrite

Boolean. whether to overwrite the existing table if it exists. Defaults to FALSE. This argument is ignored when name is NULL.

quiet

A logical value. If TRUE, suppresses any informational messages. Defaults to FALSE.

Value

Depends on the mode argument (or global preference set by ddbs_options):

  • duckspatial (default): A duckspatial_df (lazy spatial data frame) backed by dbplyr/DuckDB.

  • sf: An eagerly collected object in R memory, that will return the same data type as the sf equivalent (e.g. sf or units vector).

When name is provided, the result is also written as a table or view in DuckDB and the function returns TRUE (invisibly).

Details

These functions query structural properties of geometries:

  • ddbs_get_npoints() returns the number of points (vertices) in a geometry. For LINESTRING geometries this is the vertex count; for POLYGON types it includes all vertices of the exterior ring and any interior rings.

  • ddbs_get_ngeometries() returns the number of sub-geometries in a GEOMETRYCOLLECTION or MULTI* geometry (e.g. MULTIPOLYGON, MULTILINESTRING). Returns 1 for simple (non-collection) geometry types.

  • ddbs_get_ninterior_rings() returns the number of interior rings (holes) in a POLYGON geometry. Returns 0 for polygons without holes and NULL for non-polygon geometry types.

Examples

if (FALSE) { # \dontrun{
## load packages
library(dplyr)
library(duckspatial)

## read data
countries_ddbs <- ddbs_open_dataset(
  system.file("spatial/countries.geojson",
  package = "duckspatial")
)

## count points, sub-geometries and interior rings
ddbs_get_npoints(countries_ddbs)
ddbs_get_ngeometries(countries_ddbs)
ddbs_get_ninterior_rings(countries_ddbs)
} # }