Callback

Callbacks allow to customize the behavior of processes in mlr3 packages. The following packages implement callbacks:

• CallbackOptimization in bbotk.

• CallbackTuning in mlr3tuning.

• CallbackTorch in mlr3torch

Details

Callback is an abstract base class. A subclass inherits from Callback and adds stages as public members. Names of stages should start with "on_". For each subclass a function should be implemented to create the callback. For an example on how to implement such a function see callback_optimization() in bbotk. Callbacks are executed at stages using the function call_back(). A Context defines which information can be accessed from the callback.

Public fields

id

(character(1))
Identifier of the callback.

label

(character(1))
Label for this object. Can be used in tables, plot and text output instead of the ID.

man

(character(1))
String in the format [pkg]::[topic] pointing to a manual page for this object. Defaults to NA, but can be set by child classes.

state

(named list())
A callback can write data into the state.

Methods

Public methods

• Callback$new()

• Callback$format()

• Callback$print()

• Callback$help()

• Callback$call()

• Callback$clone()

---

Method new()

Creates a new instance of this R6 class.

Usage

Callback$new(id, label = NA_character_, man = NA_character_)

Arguments

id

(character(1))
Identifier for the new instance.

label

(character(1))
Label for the new instance.

man

(character(1))
String in the format [pkg]::[topic] pointing to a manual page for this object. The referenced help package can be opened via method $help().

---

Method format()

Helper for print outputs.

Usage

Callback$format(...)

Arguments

...

(ignored).

---

Method print()

Printer.

Usage

Callback$print(...)

Arguments

...

(ignored).

---

Method help()

Opens the corresponding help page referenced by field $man.

Usage

Callback$help()

---

Method call()

Call the specific stage for a given context.

Usage

Callback$call(stage, context)

Arguments

stage

(character(1))
stage.

context

(Context)
Context.

---

Method clone()

The objects of this class are cloneable with this method.

Usage

Callback$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.

Examples

library(R6)

# implement callback subclass
CallbackExample = R6Class("CallbackExample",
  inherit = mlr3misc::Callback,
  public = list(
    on_stage_a = NULL,
    on_stage_b = NULL,
    on_stage_c = NULL
  )
)