Selector
Selector Functions
A Selector
function is used by different PipeOp
s, most prominently PipeOpSelect
and many PipeOp
s inheriting
from PipeOpTaskPreproc
, to determine a subset of Task
s to operate on.
Even though a Selector
is a function
that can be written itself, it is preferable to use the Selector
constructors
shown here. Each of these can be called with its arguments to create a Selector
, which can then be given to the PipeOpSelect
selector
parameter, or many PipeOpTaskPreproc
s' affect_columns
parameter. See there for examples of this usage.
Usage
selector_all()selector_none()
selector_type(types)
selector_grep(pattern, ignore.case = FALSE, perl = FALSE, fixed = FALSE)
selector_name(feature_names, assert_present = FALSE)
selector_invert(selector)
selector_intersect(selector_x, selector_y)
selector_union(selector_x, selector_y)
selector_setdiff(selector_x, selector_y)
selector_missing()
selector_cardinality_greater_than(min_cardinality)
Arguments
- types
(
character
) Type of feature to select- pattern
(
character(1)
) grep pattern- ignore.case
(
logical(1)
) ignore case- perl
(
logical(1)
) perl regex- fixed
(
logical(1)
) fixed pattern instead of regex- feature_names
(
character
) Select features by exact name match.- assert_present
(
logical(1)
) Throw an error iffeature_names
are not all present in the task being operated on.- selector
- selector_x
- selector_y
- min_cardinality
(
integer
) Minimum number of levels required to be selected.
Details
A Selector
is a function
that has one input argument (commonly named task
). The function is called with the Task
that a PipeOp
is operating on. The return value of the function must be a character
vector that is a subset of the feature names present
in the Task
.
For example, a Selector
that selects all columns is
function(task) { task$feature_names }
(this is the selector_all()
-Selector
.) A Selector
that selects
all columns that have names shorter than four letters would be:
function(task) { task$feature_names[ nchar(task$feature_names) < 4 ] }
A Selector
that selects only the column "Sepal.Length"
(as in the iris task), if present, is
function(task) { intersect(task$feature_names, "Sepal.Length") }
It is preferable to use the Selector
construction functions like select_type
, select_grep
etc. if possible, instead of writing custom Selector
s.
Value
function
: A Selector
function that takes a Task
and returns the feature names to be processed.
Functions
selector_all
:selector_all
selects all features.selector_none
:selector_none
selects none of the features.selector_type
:selector_type
selects features according to type. Legal types are listed inmlr_reflections$task_feature_types
.selector_grep
:selector_grep
selects features with names matching thegrep()
pattern.selector_name
:selector_name
selects features with names matching exactly the names listed.selector_invert
:selector_invert
inverts a givenSelector
: It always selects the features that would be dropped by the otherSelector
, and drops the features that would be kept.selector_intersect
:selector_intersect
selects the intersection of twoSelector
s: Only features selected by bothSelector
s are selected in the end.selector_union
:selector_union
selects the union of twoSelector
s: Features selected by eitherSelector
are selected in the end.selector_setdiff
:selector_setdiff
selects the setdiff of twoSelector
s: Features selected byselector_x
are selected, unless they are also selected byselector_y
.selector_missing
:selector_missing
selects features with missing values.selector_cardinality_greater_than
:selector_cardinality_greater_than
selects categorical features with cardinality greater then a given threshold.
See Also
Other Selectors:
mlr_pipeops_select
Examples
# NOT RUN {
library("mlr3")
iris_task = tsk("iris")
bh_task = tsk("boston_housing")
sela = selector_all()
sela(iris_task)
sela(bh_task)
self = selector_type("factor")
self(iris_task)
self(bh_task)
selg = selector_grep("a.*i")
selg(iris_task)
selg(bh_task)
selgi = selector_invert(selg)
selgi(iris_task)
selgi(bh_task)
selgf = selector_union(selg, self)
selgf(iris_task)
selgf(bh_task)
# }