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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), 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).

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)
} # }