Query a SpatVectorProxy object

Query a SpatVectorProxy to extract a subset

# S4 method for class 'SpatVectorProxy'
query(x, start=1, n=nrow(x), vars=NULL, where=NULL, 
    extent=NULL, filter=NULL, sql=NULL, dialect="", what="")

Arguments

x

SpatVectorProxy

start

positive integer. The record to start reading at

n

positive integer. The number of records requested

vars

character. Variable names. Must be a subset of names(x)

where

character. expression like "NAME_1='California' AND ID > 3" , to subset records. Note that start and n are applied after executing the where statement

extent

Spat* object. The extent of the object is used as a spatial filter to select the geometries to read. Ignored if filter is not NULL

filter

SpatVector. Used as a spatial filter to select geometries to read (the convex hull is used for lines or points)

sql

character. Arbitrary SQL statement. If used, arguments "start", "n", "vars" and "where" are ignored

what

character indicating what to read. Either "" for geometries and attributes, or "geoms" to only read the geometries, "attributes" to only read the attributes (that are returned as a data.frame)

dialect

character. The SQL dialect to use (if any). For example: "SQLite"

See also

vect

Value

SpatVector

Examples

f <- system.file("ex/lux.shp", package="terra")
v <- vect(f, proxy=TRUE)
v
#>  class       : SpatVectorProxy
#>  geometry    : polygons 
#>  dimensions  : 12, 6  (geometries, attributes)
#>  extent      : 5.74414, 6.528252, 49.44781, 50.18162  (xmin, xmax, ymin, ymax)
#>  source      : lux.shp
#>  coord. ref. : lon/lat WGS 84 (EPSG:4326) 
#>  names       :  ID_1 NAME_1  ID_2 NAME_2  AREA   POP
#>  type        : <num>  <chr> <num>  <chr> <num> <num>

x <- query(v, vars=c("ID_2", "NAME_2"), start=5, n=2)
x
#>  class       : SpatVector 
#>  geometry    : polygons 
#>  dimensions  : 2, 2  (geometries, attributes)
#>  extent      : 5.74414, 6.528252, 49.72324, 50.03632  (xmin, xmax, ymin, ymax)
#>  source      : lux.shp
#>  coord. ref. : lon/lat WGS 84 (EPSG:4326) 
#>  names       :  ID_2     NAME_2
#>  type        : <num>      <chr>
#>  values      :     5      Wiltz
#>                    6 Echternach

query(v, vars=c("ID_2", "NAME_1", "NAME_2"), where="NAME_1='Grevenmacher' AND ID_2 > 6")
#>  class       : SpatVector 
#>  geometry    : polygons 
#>  dimensions  : 2, 3  (geometries, attributes)
#>  extent      : 6.169137, 6.516485, 49.46498, 49.75016  (xmin, xmax, ymin, ymax)
#>  source      : lux.shp
#>  coord. ref. : lon/lat WGS 84 (EPSG:4326) 
#>  names       :  ID_2       NAME_1       NAME_2
#>  type        : <num>        <chr>        <chr>
#>  values      :     7 Grevenmacher       Remich
#>                   12 Grevenmacher Grevenmacher

## with an extent
e <- ext(5.9, 6.3, 49.9, 50) 
x <- query(v, extent=e)

## with polygons
p <- as.polygons(e)
x <- query(v, filter=p)
x
#>  class       : SpatVector 
#>  geometry    : polygons 
#>  dimensions  : 4, 6  (geometries, attributes)
#>  extent      : 5.74414, 6.315773, 49.78479, 50.18162  (xmin, xmax, ymin, ymax)
#>  source      : lux.shp
#>  coord. ref. : lon/lat WGS 84 (EPSG:4326) 
#>  names       :  ID_1   NAME_1  ID_2   NAME_2  AREA       POP
#>  type        : <num>    <chr> <num>    <chr> <num>     <num>
#>  values      :     1 Diekirch     1 Clervaux   312 1.808e+04
#>                    1 Diekirch     2 Diekirch   218 3.254e+04
#>                    1 Diekirch     4  Vianden    76      5163