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Restrict which features a layer returns

Source: R/vector.R
set_filter.Rd

Both filters are set on the layer and stay set. They apply to everything read afterwards, including feature_count() and read_vector(). Passing NULL clears the filter.

Usage

set_filter(x, where, bbox)

Arguments

x

A GDALLayer object. A clause the driver cannot make sense of is not reported here: most drivers hand it to their own engine when the layer is next used, so a bad clause surfaces as a GDAL warning from feature_count() or read_vector().

where

An SQL WHERE clause without the WHERE, or NULL to clear it.

bbox

Numeric of length 4, c(xmin, ymin, xmax, ymax) in the layer's own coordinates, or NULL to clear it.

Value

The layer, invisibly.

Details

A spatial filter is what makes a large layer cheap: a driver with a spatial index uses it rather than reading every feature.

Examples

ds <- gdal_open(system.file("extdata/test.gpkg", package = "GDAL7"))
layer <- get_layer(ds, 1)
set_filter(layer, where = "population > 1e6")
feature_count(layer)
#> [1] 3
gdal_close(ds)