#' @title Survival Cox Model with Likelihood Based Boosting Learner
#' @author RaphaelS1
#' @name mlr_learners_surv.coxboost
#'
#' @description
#' Fit a Survival Cox model with a likelihood based boosting algorithm.
#' Calls [CoxBoost::CoxBoost()] from package 'CoxBoost'.
#'
#' @template learner
#' @templateVar id surv.coxboost
#'
#' @template install_coxboost
#'
#' @details
#' Use [LearnerSurvCoxboost] and [LearnerSurvCVCoxboost] for Cox boosting without and with internal
#' cross-validation of boosting step number, respectively. Tuning using the internal optimizer in
#' [LearnerSurvCVCoxboost] may be more efficient when tuning `stepno` only. However, for tuning
#' multiple hyperparameters, \CRANpkg{mlr3tuning} and [LearnerSurvCoxboost] will likely give better
#' results.
#'
#' Three prediction types are returned for this learner, using the internal
#' `predict.CoxBoost()` function:
#' 1. `lp`: a vector of linear predictors (relative risk scores), one per
#' observation.
#' 2. `crank`: same as `lp`.
#' 3. `distr`: a 2d survival matrix, with observations as rows and time points
#' as columns. The internal transformation uses the Breslow estimator to compose
#' the survival distributions from the `lp` predictions.
#'
#' @references
#' `r format_bib("binder2009boosting")`
#'
#' @template seealso_learner
#' @template example
#' @export
LearnerSurvCoxboost = R6Class("LearnerSurvCoxboost",
inherit = mlr3proba::LearnerSurv,
public = list(
#' @description
#' Creates a new instance of this [R6][R6::R6Class] class.
initialize = function() {
ps = ps(
unpen.index = p_uty(tags = "train"),
standardize = p_lgl(default = TRUE, tags = "train"),
stepno = p_int(default = 100, lower = 0, tags = "train"),
penalty = p_dbl(tags = "train"),
criterion = p_fct(default = "pscore", levels = c("pscore", "score", "hpscore", "hscore"), tags = "train"),
stepsize.factor = p_dbl(default = 1, tags = "train"),
sf.scheme = p_fct(default = "sigmoid", levels = c("sigmoid", "linear"), tags = "train"),
pendistmat = p_uty(tags = "train"),
connected.index = p_uty(tags = "train"),
x.is.01 = p_lgl(default = FALSE, tags = "train"),
return.score = p_lgl(default = TRUE, tags = "train"),
trace = p_lgl(default = FALSE, tags = "train"),
at.step = p_uty(tags = "predict")
)
super$initialize(
id = "surv.coxboost",
packages = c("mlr3extralearners", "CoxBoost", "pracma"),
feature_types = c("integer", "numeric"),
predict_types = c("distr", "crank", "lp"),
param_set = ps,
properties = c("weights", "selected_features"),
man = "mlr3extralearners::mlr_learners_surv.coxboost",
label = "Likelihood-based Boosting"
)
},
#' @description
#' Returns the set of selected features which have non-zero coefficients.
#' Calls the internal `coef.CoxBoost()` function.
#'
#' @param at_step (`integer(1)`)\cr
#' Which boosting step to get the coefficients for. If no step is given
#' (default), the final boosting step is used.
#'
#' @return (`character()`) vector of feature names.
selected_features = function(at_step = NULL) {
if (is.null(self$model)) {
stopf("No model stored")
}
coefs = invoke(stats::coef, self$model, at.step = at_step)
coefs = coefs[coefs != 0]
names(coefs)
}
),
private = list(
.train = function(task) {
pars = self$param_set$get_values(tags = "train")
if ("weights" %in% task$properties) {
pars$weights = as.numeric(task$weights$weight)
}
data = task$data()
tn = task$target_names
time = data[[tn[1L]]]
status = data[[tn[2L]]]
data = as.matrix(data[, !tn, with = FALSE])
with_package("CoxBoost", {
invoke(
CoxBoost::CoxBoost,
time = time,
status = status,
x = data,
.args = pars
)
})
},
.predict = function(task) {
pars = self$param_set$get_values(tags = "predict")
# get newdata and ensure same ordering in train and predict
newdata = as.matrix(ordered_features(task, self))
lp = as.numeric(invoke(predict,
self$model,
newdata = newdata,
.args = pars,
type = "lp"))
surv = invoke(predict,
self$model,
newdata = newdata,
.args = pars,
type = "risk",
times = sort(unique(self$model$time)))
mlr3proba::.surv_return(times = sort(unique(self$model$time)),
surv = surv,
lp = lp)
}
)
)
.extralrns_dict$add("surv.coxboost", LearnerSurvCoxboost)
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