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Union and combine geometries

Source: R/ddbs_union.R
ddbs_union_funs.Rd

Perform union and combine operations on spatial geometries in DuckDB.

  • ddbs_union() - Union all geometries into one, or perform pairwise union between two datasets

  • ddbs_union_agg() - Union geometries grouped by one or more columns

  • ddbs_combine() - Combine geometries into a MULTI-geometry without dissolving boundaries

Usage

ddbs_union(
  x,
  y = NULL,
  by_feature = FALSE,
  conn = NULL,
  conn_x = NULL,
  conn_y = NULL,
  name = NULL,
  mode = NULL,
  overwrite = FALSE,
  quiet = FALSE
)

ddbs_combine(
  x,
  conn = NULL,
  name = NULL,
  mode = NULL,
  overwrite = FALSE,
  quiet = FALSE
)

ddbs_union_agg(
  x,
  by,
  mem = FALSE,
  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.

y

Input spatial data. Can be:

  • NULL (default): performs only the union of x

  • 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

by_feature

Logical. When y is provided:

  • FALSE (default) - Union all geometries from both x and y into a single geometry

  • TRUE - Perform row-by-row union between matching features from x and y (requires same number of rows)

conn

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

conn_x

A DBIConnection object to a DuckDB database for the input x. If NULL (default), it is resolved from conn or extracted from x.

conn_y

A DBIConnection object to a DuckDB database for the input y. If NULL (default), it is resolved from conn or extracted from y.

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.

by

Character vector specifying one or more column names to group by when computing unions. Geometries will be unioned within each group. Default is NULL

mem

Logical. If TRUE, uses ST_MemUnion_Agg() instead of ST_Union_Agg() — slower but more memory efficient. Default is FALSE. Only applies to ddbs_union_agg().

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

ddbs_union(x, y, by_feature)

Performs geometric union operations that dissolve internal boundaries:

  • When y = NULL: Unions all geometries in x into a single geometry

  • When y != NULL and by_feature = FALSE: Unions all geometries from both x and y into a single geometry

  • When y != NULL and by_feature = TRUE: Performs row-wise union, pairing the first geometry from x with the first from y, second with second, etc.

ddbs_union_agg(x, by)

Groups geometries by one or more columns, then unions geometries within each group. Useful for dissolving boundaries between features that share common attributes. Set mem = TRUE to use ST_MemUnion_Agg() when memory is a constraint.

ddbs_combine(x)

Combines all geometries into a single MULTI-geometry (e.g., MULTIPOLYGON, MULTILINESTRING) without dissolving shared boundaries. This is faster than union but preserves all original geometry boundaries.

Examples

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

## create a duckdb database in memory (with spatial extension)
conn <- ddbs_create_conn(dbdir = "memory")

## read data
countries_ddbs <- ddbs_open_dataset(
  system.file("spatial/countries.geojson", 
  package = "duckspatial")
) |> 
  filter(ISO3_CODE != "ATA")

rivers_ddbs <- ddbs_open_dataset(
  system.file("spatial/rivers.geojson", 
  package = "duckspatial")
) |> 
 ddbs_transform("EPSG:4326")

## combine countries into a single MULTI-geometry
## (without solving boundaries)
combined_countries_ddbs <- ddbs_combine(countries_ddbs)

## combine countries into a single MULTI-geometry
## (solving boundaries)
union_countries_ddbs <- ddbs_union(countries_ddbs)

## union of geometries of two objects, into 1 geometry
union_countries_rivers_ddbs <- ddbs_union(countries_ddbs, rivers_ddbs)
} # }