Domain: Domain: Parameter Range without an Id

Description

A Domain object is a representation of a single dimension of a ParamSet. Domain objects are used to construct ParamSets, either through the ps() short form, through the ParamSet constructor itself, or through the ParamSet$search_space() mechanism (see to_tune()). For each of the basic parameter classes ("ParamInt", "ParamDbl", "ParamLgl", "ParamFct", and "ParamUty") there is a function constructing a Domain object (p_int(), p_dbl(), p_lgl(), p_fct(), p_uty()). They each have fitting construction arguments that control their bounds and behavior.

Domain objects are representations of parameter ranges and are intermediate objects to be used in short form constructions in to_tune() and ps(). Because of their nature, they should not be modified by the user, once constructed. The Domain object's internals are subject to change and should not be relied upon.

Usage

p_dbl(
  lower = -Inf,
  upper = Inf,
  special_vals = list(),
  default = NO_DEF,
  tags = character(),
  tolerance = sqrt(.Machine$double.eps),
  depends = NULL,
  trafo = NULL,
  logscale = FALSE,
  init,
  aggr = NULL,
  in_tune_fn = NULL,
  disable_in_tune = NULL
)
p_fct(
  levels,
  special_vals = list(),
  default = NO_DEF,
  tags = character(),
  depends = NULL,
  trafo = NULL,
  init,
  aggr = NULL,
  in_tune_fn = NULL,
  disable_in_tune = NULL
)
p_int(
  lower = -Inf,
  upper = Inf,
  special_vals = list(),
  default = NO_DEF,
  tags = character(),
  tolerance = sqrt(.Machine$double.eps),
  depends = NULL,
  trafo = NULL,
  logscale = FALSE,
  init,
  aggr = NULL,
  in_tune_fn = NULL,
  disable_in_tune = NULL
)
p_lgl(
  special_vals = list(),
  default = NO_DEF,
  tags = character(),
  depends = NULL,
  trafo = NULL,
  init,
  aggr = NULL,
  in_tune_fn = NULL,
  disable_in_tune = NULL
)
p_uty(
  custom_check = NULL,
  special_vals = list(),
  default = NO_DEF,
  tags = character(),
  depends = NULL,
  trafo = NULL,
  repr = substitute(default),
  init,
  aggr = NULL,
  in_tune_fn = NULL,
  disable_in_tune = NULL
)

Value

A Domain object.

Arguments

lower

(numeric(1))
Lower bound, can be -Inf.

upper

(numeric(1))
Upper bound can be +Inf.

special_vals

(list())
Arbitrary special values this parameter is allowed to take, to make it feasible. This allows extending the domain of the parameter. Note that these values are only used in feasibility checks, neither in generating designs nor sampling.

default

(any)
Default value. Can be from the domain of the parameter or an element of special_vals. Has value NO_DEF if no default exists. NULL can be a valid default. The value has no effect on ParamSet$values or the behavior of ParamSet$check(), $test() or $assert(). The default is intended to be used for documentation purposes. `

tags

(character())
Arbitrary tags to group and subset parameters. Some tags serve a special purpose:

"required" implies that the parameters has to be given when setting values in ParamSet.

tolerance

(numeric(1))
Initializes the $tolerance field that determines the

depends

(call | expression)
An expression indicating a requirement for the parameter that will be constructed from this. Can be given as an expression (using quote()), or the expression can be entered directly and will be parsed using NSE (see examples). The expression may be of the form <Param> == <value> or <Param> %in% <values>, which will result in dependencies according to ParamSet$add_dep(on = "<Param>", cond = CondEqual(<value>)) or ParamSet$add_dep(on = "<Param>", cond = CondAnyOf(<values>)), respectively (see CondEqual, CondAnyOf). The expression may also contain multiple conditions separated by &&.

trafo

(function)
Single argument function performing the transformation of a parameter. When the Domain is used to construct a ParamSet, this transformation will be applied to the corresponding parameter as part of the $trafo function.
Note that the trafo is not inherited by TuneTokens! Defining a parameter with e.g. p_dbl(..., trafo = ...) will not automatically give the to_tune() assigned to it a transformation. trafo only makes sense for ParamSets that get used as search spaces for optimization or tuning, it is not useful when defining domains or hyperparameter ranges of learning algorithms, because these do not use trafos.

logscale

(logical(1))
Put numeric domains on a log scale. Default FALSE. Log-scale Domains represent parameter ranges where lower and upper bounds are logarithmized, and where a trafo is added that exponentiates sampled values to the original scale. This is not the same as setting trafo = exp, because logscale = TRUE will handle parameter bounds internally: a p_dbl(1, 10, logscale = TRUE) results in a parameter that has lower bound 0, upper bound log(10), and uses exp transformation on these. Therefore, the given bounds represent the bounds after the transformation. (see examples).
p_int() with logscale = TRUE results in a continuous parameter similar to p_dbl(), not an integer-valued parameter, with bounds log(max(lower, 0.5)) ... log(upper + 1) and a trafo similar to "as.integer(exp(x))" (with additional bounds correction). The lower bound is lifted to 0.5 if lower 0 to handle the lower == 0 case. The upper bound is increased to log(upper + 1) because the trafo would otherwise almost never generate a value of upper.
When logscale is TRUE, then upper bounds may be infinite, but lower bounds should be greater than 0 for p_dbl() or greater or equal 0 for p_int().
Note that "logscale" is not inherited by TuneTokens! Defining a parameter with p_dbl(... logscale = TRUE) will not automatically give the to_tune() assigned to it log-scale. logscale only makes sense for ParamSets that get used as search spaces for optimization or tuning, it is not useful when defining domains or hyperparameter ranges of learning algorithms, because these do not use trafos.
logscale happens on a natural (e == 2.718282...) basis. Be aware that using a different base (log10()/10^, log2()/2^) is completely equivalent and does not change the values being sampled after transformation.

init

(any)
Initial value. When this is given, then the corresponding entry in ParamSet$values is initialized with this value upon construction.

aggr

(function)
Default aggregation function for a parameter. Can only be given for parameters tagged with "internal_tuning". Function with one argument, which is a list of parameter values and that returns the aggregated parameter value.

in_tune_fn

(function(domain, param_vals))
Function that converters a Domain object into a parameter value. Can only be given for parameters tagged with "internal_tuning". This function should also assert that the parameters required to enable internal tuning for the given domain are set in param_vals (such as early_stopping_rounds for XGBoost).

disable_in_tune

(named list())
The parameter values that need to be set in the ParamSet to disable the internal tuning for the parameter. For XGBoost this would e.g. be list(early_stopping_rounds = NULL).

levels

(character | atomic | list)
Allowed categorical values of the parameter. If this is not a character, then a trafo is generated that converts the names (if not given: as.character() of the values) of the levels argument to the values. This trafo is then performed before the function given as the trafo argument.

custom_check

(function())
Custom function to check the feasibility. Function which checks the input. Must return 'TRUE' if the input is valid and a character(1) with the error message otherwise. This function should not throw an error. Defaults to NULL, which means that no check is performed.

repr

(language)
Symbol to use to represent the value given in default. The deparse() of this object is used when printing the domain, in some cases.

Details

Although the levels values of a constructed p_fct() will always be character-valued, the p_fct function admits a levels argument that goes beyond this: Besides a character vector, any atomic vector or list (optionally named) may be given. (If the value is a list that is not named, the names are inferred using as.character() on the values.) The resulting Domain will correspond to a range of values given by the names of the levels argument with a trafo that maps the character names to the arbitrary values of the levels argument.

Examples

Run this code

params = ps(
  unbounded_integer = p_int(),
  bounded_double = p_dbl(0, 10),
  half_bounded_integer = p_dbl(1),
  half_bounded_double = p_dbl(upper = 1),
  double_with_trafo = p_dbl(-1, 1, trafo = exp),
  extra_double = p_dbl(0, 1, special_vals = list("xxx"), tags = "tagged"),
  factor_param = p_fct(c("a", "b", "c")),
  factor_param_with_implicit_trafo = p_fct(list(a = 1, b = 2, c = list()))
)
print(params)

params$trafo(list(
  bounded_double = 1,
  double_with_trafo = 1,
  factor_param = "c",
  factor_param_with_implicit_trafo = "c"
))

# logscale:
params = ps(x = p_dbl(1, 100, logscale = TRUE))

# The ParamSet has bounds log(1) .. log(100):
print(params)

# When generating a equidistant grid, it is equidistant within log values
grid = generate_design_grid(params, 3)
print(grid)

# But the values are on a log scale with desired bounds after trafo
print(grid$transpose())

# Integer parameters with logscale are `p_dbl()`s pre-trafo
params = ps(x = p_int(0, 10, logscale = TRUE))
print(params)

grid = generate_design_grid(params, 4)
print(grid)

# ... but get transformed to integers.
print(grid$transpose())


# internal tuning

param_set = ps(
  iters = p_int(0, Inf, tags = "internal_tuning", aggr = function(x) round(mean(unlist(x))),
    in_tune_fn = function(domain, param_vals) {
      stopifnot(domain$lower <= 1)
      stopifnot(param_vals$early_stopping == TRUE)
      domain$upper
    },
    disable_in_tune = list(early_stopping = FALSE)),
  early_stopping = p_lgl()
)
param_set$set_values(
  iters = to_tune(upper = 100, internal = TRUE),
  early_stopping = TRUE
)
param_set$convert_internal_search_space(param_set$search_space())
param_set$aggr_internal_tuned_values(
  list(iters = list(1, 2, 3))
)

param_set$disable_internal_tuning("iters")
param_set$values$early_stopping