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Count geometry components

Source: R/ddbs_queries.R
ddbs_get_npoints.Rd

Functions to count the number of points or sub-geometries 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
)

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), the function returns the result as an sf object

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.

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 and sub-geometries
ddbs_get_npoints(countries_ddbs)
ddbs_get_ngeometries(countries_ddbs)
} # }