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#' Estimate the residual variance.
#'
#' Estimate the residual variance of a regression model on a given task.
#' If a regression learner is provided instead of a model, the model is
#' trained (see [train]) first.
#'
#' @param x ([Learner] or [WrappedModel])\cr
#' Learner or wrapped model.
#' @param task ([RegrTask])\cr
#' Regression task.
#' If missing, `data` and `target` must be supplied.
#' @param data ([data.frame])\cr
#' A data frame containing the features and target variable.
#' If missing, `task` must be supplied.
#' @param target (`character(1)`)\cr
#' Name of the target variable.
#' If missing, `task` must be supplied.
#' @export
estimateResidualVariance = function(x, task, data, target) {
UseMethod("estimateResidualVariance")
}
#' @export
estimateResidualVariance.Learner = function(x, task, data, target) {
if (missing(task)) {
task = makeRegrTask(data = data, target = target)
}
estimateResidualVariance.WrappedModel(train(x, task), task)
}
#' @export
estimateResidualVariance.WrappedModel = function(x, task, data, target) {
if (missing(task)) {
task = makeRegrTask(data = data, target = target)
} else {
assertClass(task, classes = "RegrTask")
}
p = predict(x, task)
var(p$data$response - p$data$truth)
}
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