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Extract a substring of a line geometry

Source: R/ddbs_ops_unary_line.R
ddbs_line_substring.Rd

Returns the portion of a line between two fractional positions along its length

Usage

ddbs_line_substring(
  x,
  start = 0,
  end = 0.5,
  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.

start

a numeric value between 0 and 1. Specifies the starting position along the line as a proportion of its total length, where 0 is the beginning of the line. Defaults to 0.

end

a numeric value between 0 and 1. Specifies the ending position along the line as a proportion of its total length, where 1 is the end of the line. Must be greater than or equal to start. Defaults to 0.5.

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).

Examples

if (FALSE) { # \dontrun{
## load package
library(duckspatial)

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

## return the first half of each line (default)
ddbs_line_substring(rivers_ddbs)

## return the middle third of each line
ddbs_line_substring(rivers_ddbs, start = 0.33, end = 0.67)

## return the last quarter of each line
ddbs_line_substring(rivers_ddbs, start = 0.75, end = 1)
} # }