#' @title Featureless Clustering Learner
#'
#' @name mlr_learners_clust.featureless
#'
#' @description
#' A simple [LearnerClust] which randomly (but evenly) assigns observations to
#' `num_clusters` partitions (default: 1 partition).
#'
#' @templateVar id clust.featureless
#' @template learner
#'
#' @export
#' @template seealso_learner
#' @template example
LearnerClustFeatureless = R6Class("LearnerClustFeatureless",
inherit = LearnerClust,
public = list(
#' @description
#' Creates a new instance of this [R6][R6::R6Class] class.
initialize = function() {
param_set = ps(num_clusters = p_int(1L, tags = c("required", "train", "predict")))
param_set$set_values(num_clusters = 1L)
super$initialize(
id = "clust.featureless",
feature_types = c("logical", "integer", "numeric"),
predict_types = c("partition", "prob"),
param_set = param_set,
properties = c("partitional", "exclusive", "complete", "missings"),
man = "mlr3cluster::mlr_learners_clust.featureless",
label = "Featureless Clustering"
)
}
),
private = list(
.train = function(task) {
pv = self$param_set$get_values(tags = "train")
k = pv$num_clusters
n = task$nrow
if (k > n) {
stopf("number of clusters must lie between 1 and `nrow(data)`.")
}
partition = chunk(n, n_chunks = k)
if (self$save_assignments) {
self$assignments = partition
}
set_class(
list(clustering = partition, features = task$feature_names),
"clust.featureless_model"
)
},
.predict = function(task) {
pv = self$param_set$get_values(tags = "predict")
n = task$nrow
k = pv$num_clusters
partition = chunk(n, n_chunks = k)
prob = NULL
if (self$predict_type == "prob") {
prob = matrix(runif(n * k), nrow = n, ncol = k)
prob = prob / rowSums(prob)
# reorder rows so that the max probability corresponds to
# the selected partition in `partition`
prob = do.call(rbind, map(seq_along(partition), function(i) {
x = prob[i, , drop = TRUE]
pos = which_max(x)
if (pos == i) x else append(x[-pos], x[pos], after = partition[i] - 1L)
}))
}
PredictionClust$new(task = task, partition = partition, prob = prob)
}
)
)
#' @include zzz.R
register_learner("clust.featureless", LearnerClustFeatureless)
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