vapour_read_fields: Read feature field data

In vapour: Access to the 'Geospatial Data Abstraction Library' ('GDAL')

Read feature field data

Description

Read features fields (attributes), optionally after SQL execution.

Usage

vapour_read_fields(
  dsource,
  layer = 0L,
  sql = "",
  limit_n = NULL,
  skip_n = 0,
  extent = NA
)

vapour_read_attributes(
  dsource,
  layer = 0L,
  sql = "",
  limit_n = NULL,
  skip_n = 0,
  extent = NA
)

Arguments

dsource	data source name (path to file, connection string, URL)
layer	integer of layer to work with, defaults to the first (0) or the name of the layer
sql	if not empty this is executed against the data source (layer will be ignored)
limit_n	an arbitrary limit to the number of features scanned
skip_n	an arbitrary number of features to skip
extent	apply an arbitrary extent, only when 'sql' used (must be 'ex = c(xmin, xmax, ymin, ymax)' but sp bbox, sf bbox, and raster extent also accepted)

Details

Internal types are not fully supported, there are straightforward conversions for numeric, integer (32-bit) and string types. Date, Time, DateTime are returned as character, and Integer64 is returned as numeric.

Value

list of vectors one for each field in the source, each will be the same length which will depend on the values of 'skip_n', 'limit_n', 'sql', and the available records in the source. The types will be raw, numeric, integer, character, logical depending on the available mapping to the types in the source for the data there to R's native vectors.

Examples

file <- "list_locality_postcode_meander_valley.tab"
mvfile <- system.file(file.path("extdata/tab", file), package="vapour")
att <- vapour_read_fields(mvfile)
str(att)
sq <- "SELECT * FROM list_locality_postcode_meander_valley WHERE FID < 5"
(att <- vapour_read_fields(mvfile, sql = sq))
pfile <- "list_locality_postcode_meander_valley.tab"
dsource <- system.file(file.path("extdata/tab", pfile), package="vapour")
SQL <- "SELECT NAME FROM list_locality_postcode_meander_valley WHERE POSTCODE < 7300"
vapour_read_fields(dsource, sql = SQL)

vapour documentation built on June 22, 2024, 10:01 a.m.