Skip to contents

Access processing output

Source: R/qgis-result.R
qgis_extract_output.Rd

These functions extract one output element from the result of qgis_run_algorithm(), potentially more than one in the case of qgis_extract_output_by_class(). An output element can be extracted based on its name, its position in the printed qgis_result object returned by qgis_run_algorithm(), or its class.

qgis_extract_output() is an alias to qgis_extract_output_by_name().

Usage

qgis_extract_output_by_name(x, name = "OUTPUT", first = TRUE)

qgis_extract_output(x, name = "OUTPUT", first = TRUE)

qgis_extract_output_by_position(x, which)

qgis_extract_output_by_class(x, class, single = TRUE)

Arguments

x

A qgis_result object returned by qgis_run_algorithm().

name

The name of an output.

first

Logical. Should qgis_extract_output_by_name() fall back to the first output element if the default OUTPUT or output element is not available? Only takes effect if name is equal to OUTPUT or output, but not found.

which

The index of an output.

class

Character vector of classes. At least one class must be inherited by an element of x for that element to be selected.

single

Logical. Ensures the selection of a single output in qgis_extract_output_by_class(). The OUTPUT or output element is taken if available and on condition that it inherits a specified class; otherwise falls back to the first element that inherits a specified class.

Value

A qgis_output* object.

See also

Other topics about accessing or managing processing results: qgis_as_raster(), qgis_as_terra(), qgis_clean_result(), qgis_result_status(), st_as_sf, st_as_stars

Examples

result <- qgis_run_algorithm(
  "native:buffer",
  INPUT = system.file("longlake/longlake_depth.gpkg", package = "qgisprocess"),
  DISTANCE = 10
)
#> Argument `SEGMENTS` is unspecified (using QGIS default value).
#> Using `END_CAP_STYLE = "Round"`
#> Using `JOIN_STYLE = "Round"`
#> Argument `MITER_LIMIT` is unspecified (using QGIS default value).
#> Argument `DISSOLVE` is unspecified (using QGIS default value).
#> Argument `SEPARATE_DISJOINT` is unspecified (using QGIS default value).
#> Using `OUTPUT = qgis_tmp_vector()`

# the print() method of a qgis_result only prints its output elements:
result
#> <Result of `qgis_run_algorithm("native:buffer", ...)`>
#> List of 1
#>  $ OUTPUT: 'qgis_outputVector' chr "/tmp/Rtmp7nb1k0/file2b044d88ac6c/file2b04b4b7454.gpkg"

# nevertheless, more elements are included:
length(result)
#> [1] 5
names(result)
#> [1] "OUTPUT"           ".algorithm"       ".args"            ".raw_json_input" 
#> [5] ".processx_result"

# extract the output element 'OUTPUT':
qgis_extract_output(result)
#> [1] "/tmp/Rtmp7nb1k0/file2b044d88ac6c/file2b04b4b7454.gpkg"
#> attr(,"class")
#> [1] "qgis_outputVector"