diff --git a/DESCRIPTION b/DESCRIPTION
index b5a5a56e8..0c004295e 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,6 +1,6 @@
 Package: mlr3pipelines
 Title: Preprocessing Operators and Pipelines for 'mlr3'
-Version: 0.1.0
+Version: 0.1.0.9000
 Authors@R:
     c(person(given = "Martin",
              family = "Binder",
@@ -89,11 +89,13 @@ Collate:
     'PipeOpClassBalancing.R'
     'PipeOpClassifAvg.R'
     'PipeOpColApply.R'
+    'PipeOpCollapseFactors.R'
     'PipeOpCopy.R'
     'PipeOpEncode.R'
     'PipeOpEncodeLmer.R'
     'PipeOpFeatureUnion.R'
     'PipeOpFilter.R'
+    'PipeOpFixFactors.R'
     'PipeOpHistBin.R'
     'PipeOpICA.R'
     'PipeOpImpute.R'
diff --git a/NAMESPACE b/NAMESPACE
index 32c2750d1..cef50f0e6 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -26,12 +26,14 @@ export(PipeOpChunk)
 export(PipeOpClassBalancing)
 export(PipeOpClassifAvg)
 export(PipeOpColApply)
+export(PipeOpCollapseFactors)
 export(PipeOpCopy)
 export(PipeOpEncode)
 export(PipeOpEncodeLmer)
 export(PipeOpEnsemble)
 export(PipeOpFeatureUnion)
 export(PipeOpFilter)
+export(PipeOpFixFactors)
 export(PipeOpHistBin)
 export(PipeOpICA)
 export(PipeOpImpute)
diff --git a/R/PipeOpCollapseFactors.R b/R/PipeOpCollapseFactors.R
new file mode 100644
index 000000000..203e208fa
--- /dev/null
+++ b/R/PipeOpCollapseFactors.R
@@ -0,0 +1,136 @@
+#' @title PipeOpCollapseFactors
+#'
+#' @usage NULL
+#' @name mlr_pipeops_collapsefactors
+#' @format [`R6Class`] object inheriting from [`PipeOpTaskPreprocSimple`]/[`PipeOpTaskPreproc`]/[`PipeOp`].
+#'
+#' @description
+#' Collapses factors of type `factor`, `ordered`: Collapses the rarest factors in the
+#' training samples, until `target_level_count` levels remain. Levels that have prevalence above `no_collapse_above_prevalence`
+#'  are retained, however. For `factor` variables, these are collapsed to the next larger level, for `ordered` variables,
+#' rare variables are collapsed to the neighbouring class, whichever has fewer samples.
+#'
+#' Levels not seen during training are not touched during prediction; Therefore it is useful to combine this with the
+#' [`PipeOpFixFactors`].
+#'
+#' @section Construction:
+#' ```
+#' PipeOpCollapseFactors$new(id = "collapsefactors", param_vals = list())
+#' ```
+#' * `id` :: `character(1)`\cr
+#'   Identifier of resulting object, default `"collapsefactors"`.
+#' * `param_vals` :: named `list`\cr
+#'   List of hyperparameter settings, overwriting the hyperparameter settings that would otherwise be set during construction. Default `list()`.
+#'
+#' @section Input and Output Channels:
+#' Input and output channels are inherited from [`PipeOpTaskPreproc`].
+#'
+#' The output is the input [`Task`][mlr3::Task] with rare affected `factor` and `ordered` feature levels collapsed.
+#'
+#' @section State:
+#' The `$state` is a named `list` with the `$state` elements inherited from [`PipeOpTaskPreproc`], as well as:
+#' * `collapse_map` :: named `list` of named `list` of `character`\cr
+#'   List of factor level maps. For each factor, `collapse_map` contains a named `list` that indicates what levels
+#'   of the input task get mapped to what levels of the output task. If `collapse_map` has an entry `feat_1` with
+#'   an entry `a = c("x", "y")`, it means that levels `"x"` and `"y"` get collapsed to level `"a"` in feature `"feat_1"`.
+#'
+#' @section Parameters:
+#' The parameters are the parameters inherited from [`PipeOpTaskPreproc`], as well as:
+#' * `no_collapse_above_prevalence`  :: `numeric(1)` \cr
+#'   Fraction of samples below which factor levels get collapsed. Default is 1, which causes all levels
+#'   to be collapsed until `target_level_count` remain.
+#' * `target_level_count`  :: `integer(1)` \cr
+#'   Number of levels to retain. Default is 2.
+#'
+#' @section Internals:
+#' Makes use of the fact that `levels(fact_var) = list(target1 = c("source1", "source2"), target2 = "source2")` causes
+#' renaming of level `"source1"` and `"source2"` both to `"target1"`, and also `"source2"` to `"target2"`.
+#'
+#' @section Methods:
+#' Only methods inherited from [`PipeOpTaskPreprocSimple`]/[`PipeOpTaskPreproc`]/[`PipeOp`].
+#'
+#' @family PipeOps
+#' @include PipeOpTaskPreproc.R
+#' @export
+#' @examples
+#' library("mlr3")
+PipeOpCollapseFactors = R6Class("PipeOpCollapseFactors",
+  inherit = PipeOpTaskPreprocSimple,
+  public = list(
+    initialize = function(id = "collapsefactors", param_vals = list()) {
+      ps = ParamSet$new(params = list(
+        ParamDbl$new("no_collapse_above_prevalence", 0, 1, tags = c("train", "predict")),
+        ParamInt$new("target_level_count", 2, tags = c("train", "predict"))
+      ))
+      ps$values = list(no_collapse_above_prevalence = 1, target_level_count = 2)
+      super$initialize(id, param_set = ps, param_vals = param_vals)
+    },
+
+    select_cols = function(task) {
+      task$feature_types[get("type") %in% c("factor", "ordered"), get("id")]
+    },
+
+    get_state = function(task) {
+      # get the levels of the training task
+      dt = task$data(cols = self$select_cols(task))
+
+      keep_fraction = self$param_set$values$no_collapse_above_prevalence
+      target_count = self$param_set$values$target_level_count
+
+      collapse_map = sapply(dt, function(d) {
+        if (all(is.na(d))) {
+          return(NULL)
+        }
+        if (length(levels(d)) <= target_count) {
+          return(NULL)
+        }
+        dtable = table(d)
+        fractions = sort(dtable, decreasing = TRUE) / sum(!is.na(d))
+        keep_fraction = names(fractions)[fractions >= keep_fraction]
+        keep_count = names(fractions)[seq_len(target_count)]  # at this point we know there are more levels than target_count
+        keep = union(keep_fraction, keep_count)
+        dont_keep = setdiff(levels(d), keep)
+        if (is.ordered(d)) {
+          cmap = setNames(as.list(levels(d)), levels(d))
+          for (eliminating in dont_keep) {
+            position = match(eliminating, names(cmap))
+            if (position == 1) {
+              cmap[[2]] = c(cmap[[2]], eliminating)
+            } else if (position == length(cmap) || dtable[position - 1] < dtable[position + 1]) {
+              cmap[[position - 1]] = c(cmap[[position - 1]], eliminating)
+            } else {
+              cmap[[position + 1]] = c(cmap[[position + 1]], eliminating)
+            }
+            dtable = dtable[-position]
+            cmap[[position]] = NULL
+          }
+        } else {
+          cmap = setNames(as.list(keep), keep)
+          lowest_kept = keep[length(keep)]
+          cmap[[lowest_kept]] = c(lowest_kept, dont_keep)
+        }
+        cmap
+      }, simplify = FALSE)
+
+      list(collapse_map = discard(collapse_map, is.null))
+    },
+
+    transform = function(task) {
+      cmaplist = self$state$collapse_map
+      dt = task$data(cols = names(cmaplist))
+
+      for (n in names(cmaplist)) {
+        # don't touch unseen factor levels
+        new_lvls = setdiff(levels(dt[[n]]), unlist(cmaplist[[n]], use.names = FALSE))
+        all_lvls = c(cmaplist[[n]], setNames(as.list(new_lvls), new_lvls))
+        levels(dt[[n]]) = c(
+          all_lvls[intersect(levels(dt[[n]]), names(all_lvls))],  # keep all levels in their order, if they were present before
+          all_lvls[setdiff(names(all_lvls), levels(dt[[n]]))]     # levels that are missing now get sorted to the back.
+        )
+      }
+      task$select(setdiff(task$feature_names, names(cmaplist)))$cbind(dt)
+    }
+  )
+)
+
+mlr_pipeops$add("collapsefactors", PipeOpCollapseFactors)
diff --git a/R/PipeOpFixFactors.R b/R/PipeOpFixFactors.R
new file mode 100644
index 000000000..1ab58f7ad
--- /dev/null
+++ b/R/PipeOpFixFactors.R
@@ -0,0 +1,106 @@
+#' @title PipeOpFixFactors
+#'
+#' @usage NULL
+#' @name mlr_pipeops_fixfactors
+#' @format [`R6Class`] object inheriting from [`PipeOpTaskPreprocSimple`]/[`PipeOpTaskPreproc`]/[`PipeOp`].
+#'
+#' @description
+#' Fixes factors of type `factor`, `ordered`: Makes sure the factor levels
+#' during prediction are the same as during training; possibly dropping empty
+#' training factor levels before.
+#'
+#' Note this may introduce *missing values* during prediction if unseen factor levels are found.
+#'
+#' @section Construction:
+#' ```
+#' PipeOpFixFactors$new(id = "fixfactors", param_vals = list())
+#' ```
+#' * `id` :: `character(1)`\cr
+#'   Identifier of resulting object, default `"fixfactors"`.
+#' * `param_vals` :: named `list`\cr
+#'   List of hyperparameter settings, overwriting the hyperparameter settings that would otherwise be set during construction. Default `list()`.
+#'
+#' @section Input and Output Channels:
+#' Input and output channels are inherited from [`PipeOpTaskPreproc`].
+#'
+#' The output is the input [`Task`][mlr3::Task] with all affected `factor` and `ordered` feature levels fixed.
+#'
+#' @section State:
+#' The `$state` is a named `list` with the `$state` elements inherited from [`PipeOpTaskPreproc`], as well as:
+#' * `levels` :: named `list` of `character`\cr
+#'   List of factor levels of each affected `factor` or `ordered` feature that will be fixed.
+#'
+#' @section Parameters:
+#' The parameters are the parameters inherited from [`PipeOpTaskPreproc`], as well as:
+#' * `droplevels`  :: `logical(1)` \cr
+#'   Whether to drop empty factor levels of the training task. Default `TRUE`
+#'
+#' @section Internals:
+#' Changes factor levels of columns and attaches them with a new `data.table` backend and the virtual `cbind()` backend.
+#'
+#' @section Methods:
+#' Only methods inherited from [`PipeOpTaskPreprocSimple`]/[`PipeOpTaskPreproc`]/[`PipeOp`].
+#'
+#' @family PipeOps
+#' @include PipeOpTaskPreproc.R
+#' @export
+#' @examples
+#' library("mlr3")
+PipeOpFixFactors = R6Class("PipeOpFixFactors",
+  inherit = PipeOpTaskPreprocSimple,
+  public = list(
+    initialize = function(id = "fixfactors", param_vals = list()) {
+      ps = ParamSet$new(params = list(
+        ParamLgl$new("droplevels", tags = c("train", "predict"))
+      ))
+      ps$values = list(droplevels = TRUE)
+      super$initialize(id, param_set = ps, param_vals = param_vals)
+    },
+
+    select_cols = function(task) {
+      task$feature_types[get("type") %in% c("factor", "ordered"), get("id")]
+    },
+
+    get_state = function(task) {
+      # get the levels of the training task
+      dt = task$data(cols = self$select_cols(task))
+      if (self$param_set$values$droplevels) {
+        dt = droplevels(dt)
+      }
+      list(levels = lapply(dt, function(x) levels(x)))  # explicitly access the "levels" function
+    },
+
+    transform = function(task) {
+      dt = task$data(cols = names(self$state$levels))
+
+      # check which levels are actually different during training and prediction
+      needs_adjustment = as.logical(imap(self$state$levels, function(lvx, id) {
+        !identical(lvx, levels(dt[[id]]))
+      }))
+
+      if (!any(needs_adjustment)) {
+        return(task)
+      }
+
+      changed_cols = as.data.table(imap(self$state$levels[needs_adjustment], function(lvx, id) {
+        x = dt[[id]]
+        if (is.ordered(x)) {
+          ordered(x, levels = lvx)
+        } else {
+          factor(x, levels = lvx)
+        }
+      }))
+      task$select(setdiff(task$feature_names, colnames(changed_cols)))$cbind(changed_cols)
+    }
+  )
+)
+
+mlr_pipeops$add("fixfactors", PipeOpFixFactors)
+
+# FIXME: from mlr3; should probably go to mlr3misc
+ujoin = function (x, y, key) {
+  cn = setdiff(intersect(names(x), names(y)), key)
+  expr = parse(text = paste0("`:=`(", paste0(sprintf("%1$s=i.%1$s",
+    cn), collapse = ","), ")"))
+  x[y, eval(expr), on = key]
+}
diff --git a/man/PipeOp.Rd b/man/PipeOp.Rd
index c4a7c8f4d..706097fcf 100644
--- a/man/PipeOp.Rd
+++ b/man/PipeOp.Rd
@@ -207,11 +207,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/PipeOpEnsemble.Rd b/man/PipeOpEnsemble.Rd
index 59f6cb427..e19157e50 100644
--- a/man/PipeOpEnsemble.Rd
+++ b/man/PipeOpEnsemble.Rd
@@ -97,11 +97,13 @@ Other PipeOps: \code{\link{PipeOpImpute}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/PipeOpImpute.Rd b/man/PipeOpImpute.Rd
index fcf82cb16..7a6c8de43 100644
--- a/man/PipeOpImpute.Rd
+++ b/man/PipeOpImpute.Rd
@@ -118,11 +118,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/PipeOpTaskPreproc.Rd b/man/PipeOpTaskPreproc.Rd
index c11c5189b..3ed96fcbb 100644
--- a/man/PipeOpTaskPreproc.Rd
+++ b/man/PipeOpTaskPreproc.Rd
@@ -177,11 +177,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops.Rd b/man/mlr_pipeops.Rd
index 20c40e366..f5c380ba1 100644
--- a/man/mlr_pipeops.Rd
+++ b/man/mlr_pipeops.Rd
@@ -68,11 +68,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_boxcox.Rd b/man/mlr_pipeops_boxcox.Rd
index 28e5eb628..92143a59d 100644
--- a/man/mlr_pipeops_boxcox.Rd
+++ b/man/mlr_pipeops_boxcox.Rd
@@ -83,11 +83,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_branch.Rd b/man/mlr_pipeops_branch.Rd
index 69477b4ba..a8092b7f1 100644
--- a/man/mlr_pipeops_branch.Rd
+++ b/man/mlr_pipeops_branch.Rd
@@ -103,11 +103,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_chunk.Rd b/man/mlr_pipeops_chunk.Rd
index 339ea820a..954e47836 100644
--- a/man/mlr_pipeops_chunk.Rd
+++ b/man/mlr_pipeops_chunk.Rd
@@ -82,11 +82,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_classbalancing.Rd b/man/mlr_pipeops_classbalancing.Rd
index dd20d3420..137319bf2 100644
--- a/man/mlr_pipeops_classbalancing.Rd
+++ b/man/mlr_pipeops_classbalancing.Rd
@@ -121,11 +121,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_chunk}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_classifavg.Rd b/man/mlr_pipeops_classifavg.Rd
index 534b0437a..b3b66b581 100644
--- a/man/mlr_pipeops_classifavg.Rd
+++ b/man/mlr_pipeops_classifavg.Rd
@@ -89,11 +89,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_chunk}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_colapply.Rd b/man/mlr_pipeops_colapply.Rd
index c22e706bd..7c489185a 100644
--- a/man/mlr_pipeops_colapply.Rd
+++ b/man/mlr_pipeops_colapply.Rd
@@ -112,11 +112,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_chunk}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_collapsefactors.Rd b/man/mlr_pipeops_collapsefactors.Rd
new file mode 100644
index 000000000..d0c7fb063
--- /dev/null
+++ b/man/mlr_pipeops_collapsefactors.Rd
@@ -0,0 +1,118 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/PipeOpCollapseFactors.R
+\docType{data}
+\name{mlr_pipeops_collapsefactors}
+\alias{mlr_pipeops_collapsefactors}
+\alias{PipeOpCollapseFactors}
+\title{PipeOpCollapseFactors}
+\format{\code{\link{R6Class}} object inheriting from \code{\link{PipeOpTaskPreprocSimple}}/\code{\link{PipeOpTaskPreproc}}/\code{\link{PipeOp}}.}
+\description{
+Collapses factors of type \code{factor}, \code{ordered}: Collapses the rarest factors in the
+training samples, until \code{target_level_count} levels remain. Levels that have prevalence above \code{no_collapse_above_prevalence}
+are retained, however. For \code{factor} variables, these are collapsed to the next larger level, for \code{ordered} variables,
+rare variables are collapsed to the neighbouring class, whichever has fewer samples.
+
+Levels not seen during training are not touched during prediction; Therefore it is useful to combine this with the
+\code{\link{PipeOpFixFactors}}.
+}
+\section{Construction}{
+\preformatted{PipeOpCollapseFactors$new(id = "collapsefactors", param_vals = list())
+}
+\itemize{
+\item \code{id} :: \code{character(1)}\cr
+Identifier of resulting object, default \code{"collapsefactors"}.
+\item \code{param_vals} :: named \code{list}\cr
+List of hyperparameter settings, overwriting the hyperparameter settings that would otherwise be set during construction. Default \code{list()}.
+}
+}
+
+\section{Input and Output Channels}{
+
+Input and output channels are inherited from \code{\link{PipeOpTaskPreproc}}.
+
+The output is the input \code{\link[mlr3:Task]{Task}} with rare affected \code{factor} and \code{ordered} feature levels collapsed.
+}
+
+\section{State}{
+
+The \code{$state} is a named \code{list} with the \code{$state} elements inherited from \code{\link{PipeOpTaskPreproc}}, as well as:
+\itemize{
+\item \code{collapse_map} :: named \code{list} of named \code{list} of \code{character}\cr
+List of factor level maps. For each factor, \code{collapse_map} contains a named \code{list} that indicates what levels
+of the input task get mapped to what levels of the output task. If \code{collapse_map} has an entry \code{feat_1} with
+an entry \code{a = c("x", "y")}, it means that levels \code{"x"} and \code{"y"} get collapsed to level \code{"a"} in feature \code{"feat_1"}.
+}
+}
+
+\section{Parameters}{
+
+The parameters are the parameters inherited from \code{\link{PipeOpTaskPreproc}}, as well as:
+\itemize{
+\item \code{no_collapse_above_prevalence}  :: \code{numeric(1)} \cr
+Fraction of samples below which factor levels get collapsed. Default is 1, which causes all levels
+to be collapsed until \code{target_level_count} remain.
+\item \code{target_level_count}  :: \code{integer(1)} \cr
+Number of levels to retain. Default is 2.
+}
+}
+
+\section{Internals}{
+
+Makes use of the fact that \code{levels(fact_var) = list(target1 = c("source1", "source2"), target2 = "source2")} causes
+renaming of level \code{"source1"} and \code{"source2"} both to \code{"target1"}, and also \code{"source2"} to \code{"target2"}.
+}
+
+\section{Methods}{
+
+Only methods inherited from \code{\link{PipeOpTaskPreprocSimple}}/\code{\link{PipeOpTaskPreproc}}/\code{\link{PipeOp}}.
+}
+
+\examples{
+library("mlr3")
+}
+\seealso{
+Other PipeOps: \code{\link{PipeOpEnsemble}},
+  \code{\link{PipeOpImpute}},
+  \code{\link{PipeOpTaskPreproc}}, \code{\link{PipeOp}},
+  \code{\link{mlr_pipeops_boxcox}},
+  \code{\link{mlr_pipeops_branch}},
+  \code{\link{mlr_pipeops_chunk}},
+  \code{\link{mlr_pipeops_classbalancing}},
+  \code{\link{mlr_pipeops_classifavg}},
+  \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_copy}},
+  \code{\link{mlr_pipeops_encodelmer}},
+  \code{\link{mlr_pipeops_encode}},
+  \code{\link{mlr_pipeops_featureunion}},
+  \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
+  \code{\link{mlr_pipeops_histbin}},
+  \code{\link{mlr_pipeops_ica}},
+  \code{\link{mlr_pipeops_imputehist}},
+  \code{\link{mlr_pipeops_imputemean}},
+  \code{\link{mlr_pipeops_imputemedian}},
+  \code{\link{mlr_pipeops_imputenewlvl}},
+  \code{\link{mlr_pipeops_imputesample}},
+  \code{\link{mlr_pipeops_kernelpca}},
+  \code{\link{mlr_pipeops_learner}},
+  \code{\link{mlr_pipeops_missind}},
+  \code{\link{mlr_pipeops_modelmatrix}},
+  \code{\link{mlr_pipeops_mutate}},
+  \code{\link{mlr_pipeops_nop}},
+  \code{\link{mlr_pipeops_pca}},
+  \code{\link{mlr_pipeops_quantilebin}},
+  \code{\link{mlr_pipeops_regravg}},
+  \code{\link{mlr_pipeops_removeconstants}},
+  \code{\link{mlr_pipeops_scalemaxabs}},
+  \code{\link{mlr_pipeops_scalerange}},
+  \code{\link{mlr_pipeops_scale}},
+  \code{\link{mlr_pipeops_select}},
+  \code{\link{mlr_pipeops_smote}},
+  \code{\link{mlr_pipeops_spatialsign}},
+  \code{\link{mlr_pipeops_subsample}},
+  \code{\link{mlr_pipeops_unbranch}},
+  \code{\link{mlr_pipeops_yeojohnson}},
+  \code{\link{mlr_pipeops}}
+}
+\concept{PipeOps}
+\keyword{datasets}
diff --git a/man/mlr_pipeops_copy.Rd b/man/mlr_pipeops_copy.Rd
index ec94a1d5f..381171f46 100644
--- a/man/mlr_pipeops_copy.Rd
+++ b/man/mlr_pipeops_copy.Rd
@@ -102,10 +102,12 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_encode.Rd b/man/mlr_pipeops_encode.Rd
index 9938220c9..654ce0cab 100644
--- a/man/mlr_pipeops_encode.Rd
+++ b/man/mlr_pipeops_encode.Rd
@@ -105,10 +105,12 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_encodelmer.Rd b/man/mlr_pipeops_encodelmer.Rd
index 595dfd71a..917e0c326 100644
--- a/man/mlr_pipeops_encodelmer.Rd
+++ b/man/mlr_pipeops_encodelmer.Rd
@@ -108,10 +108,12 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_featureunion.Rd b/man/mlr_pipeops_featureunion.Rd
index 9c72ad4a7..8e60ac8bd 100644
--- a/man/mlr_pipeops_featureunion.Rd
+++ b/man/mlr_pipeops_featureunion.Rd
@@ -98,10 +98,12 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_filter.Rd b/man/mlr_pipeops_filter.Rd
index 351928259..2bef134c5 100644
--- a/man/mlr_pipeops_filter.Rd
+++ b/man/mlr_pipeops_filter.Rd
@@ -126,10 +126,12 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_fixfactors.Rd b/man/mlr_pipeops_fixfactors.Rd
new file mode 100644
index 000000000..6d93f1c40
--- /dev/null
+++ b/man/mlr_pipeops_fixfactors.Rd
@@ -0,0 +1,110 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/PipeOpFixFactors.R
+\docType{data}
+\name{mlr_pipeops_fixfactors}
+\alias{mlr_pipeops_fixfactors}
+\alias{PipeOpFixFactors}
+\title{PipeOpFixFactors}
+\format{\code{\link{R6Class}} object inheriting from \code{\link{PipeOpTaskPreprocSimple}}/\code{\link{PipeOpTaskPreproc}}/\code{\link{PipeOp}}.}
+\description{
+Fixes factors of type \code{factor}, \code{ordered}: Makes sure the factor levels
+during prediction are the same as during training; possibly dropping empty
+training factor levels before.
+
+Note this may introduce \emph{missing values} during prediction if unseen factor levels are found.
+}
+\section{Construction}{
+\preformatted{PipeOpFixFactors$new(id = "fixfactors", param_vals = list())
+}
+\itemize{
+\item \code{id} :: \code{character(1)}\cr
+Identifier of resulting object, default \code{"fixfactors"}.
+\item \code{param_vals} :: named \code{list}\cr
+List of hyperparameter settings, overwriting the hyperparameter settings that would otherwise be set during construction. Default \code{list()}.
+}
+}
+
+\section{Input and Output Channels}{
+
+Input and output channels are inherited from \code{\link{PipeOpTaskPreproc}}.
+
+The output is the input \code{\link[mlr3:Task]{Task}} with all affected \code{factor} and \code{ordered} feature levels fixed.
+}
+
+\section{State}{
+
+The \code{$state} is a named \code{list} with the \code{$state} elements inherited from \code{\link{PipeOpTaskPreproc}}, as well as:
+\itemize{
+\item \code{levels} :: named \code{list} of \code{character}\cr
+List of factor levels of each affected \code{factor} or \code{ordered} feature that will be fixed.
+}
+}
+
+\section{Parameters}{
+
+The parameters are the parameters inherited from \code{\link{PipeOpTaskPreproc}}, as well as:
+\itemize{
+\item \code{droplevels}  :: \code{logical(1)} \cr
+Whether to drop empty factor levels of the training task. Default \code{TRUE}
+}
+}
+
+\section{Internals}{
+
+Changes factor levels of columns and attaches them with a new \code{data.table} backend and the virtual \code{cbind()} backend.
+}
+
+\section{Methods}{
+
+Only methods inherited from \code{\link{PipeOpTaskPreprocSimple}}/\code{\link{PipeOpTaskPreproc}}/\code{\link{PipeOp}}.
+}
+
+\examples{
+library("mlr3")
+}
+\seealso{
+Other PipeOps: \code{\link{PipeOpEnsemble}},
+  \code{\link{PipeOpImpute}},
+  \code{\link{PipeOpTaskPreproc}}, \code{\link{PipeOp}},
+  \code{\link{mlr_pipeops_boxcox}},
+  \code{\link{mlr_pipeops_branch}},
+  \code{\link{mlr_pipeops_chunk}},
+  \code{\link{mlr_pipeops_classbalancing}},
+  \code{\link{mlr_pipeops_classifavg}},
+  \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
+  \code{\link{mlr_pipeops_copy}},
+  \code{\link{mlr_pipeops_encodelmer}},
+  \code{\link{mlr_pipeops_encode}},
+  \code{\link{mlr_pipeops_featureunion}},
+  \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_histbin}},
+  \code{\link{mlr_pipeops_ica}},
+  \code{\link{mlr_pipeops_imputehist}},
+  \code{\link{mlr_pipeops_imputemean}},
+  \code{\link{mlr_pipeops_imputemedian}},
+  \code{\link{mlr_pipeops_imputenewlvl}},
+  \code{\link{mlr_pipeops_imputesample}},
+  \code{\link{mlr_pipeops_kernelpca}},
+  \code{\link{mlr_pipeops_learner}},
+  \code{\link{mlr_pipeops_missind}},
+  \code{\link{mlr_pipeops_modelmatrix}},
+  \code{\link{mlr_pipeops_mutate}},
+  \code{\link{mlr_pipeops_nop}},
+  \code{\link{mlr_pipeops_pca}},
+  \code{\link{mlr_pipeops_quantilebin}},
+  \code{\link{mlr_pipeops_regravg}},
+  \code{\link{mlr_pipeops_removeconstants}},
+  \code{\link{mlr_pipeops_scalemaxabs}},
+  \code{\link{mlr_pipeops_scalerange}},
+  \code{\link{mlr_pipeops_scale}},
+  \code{\link{mlr_pipeops_select}},
+  \code{\link{mlr_pipeops_smote}},
+  \code{\link{mlr_pipeops_spatialsign}},
+  \code{\link{mlr_pipeops_subsample}},
+  \code{\link{mlr_pipeops_unbranch}},
+  \code{\link{mlr_pipeops_yeojohnson}},
+  \code{\link{mlr_pipeops}}
+}
+\concept{PipeOps}
+\keyword{datasets}
diff --git a/man/mlr_pipeops_histbin.Rd b/man/mlr_pipeops_histbin.Rd
index 78dd6d32f..9cfb53693 100644
--- a/man/mlr_pipeops_histbin.Rd
+++ b/man/mlr_pipeops_histbin.Rd
@@ -82,11 +82,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
   \code{\link{mlr_pipeops_imputemean}},
diff --git a/man/mlr_pipeops_ica.Rd b/man/mlr_pipeops_ica.Rd
index 6000c170e..bed7d740d 100644
--- a/man/mlr_pipeops_ica.Rd
+++ b/man/mlr_pipeops_ica.Rd
@@ -110,11 +110,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_imputehist}},
   \code{\link{mlr_pipeops_imputemean}},
diff --git a/man/mlr_pipeops_imputehist.Rd b/man/mlr_pipeops_imputehist.Rd
index d9eac8b36..7ef6c2977 100644
--- a/man/mlr_pipeops_imputehist.Rd
+++ b/man/mlr_pipeops_imputehist.Rd
@@ -71,11 +71,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputemean}},
diff --git a/man/mlr_pipeops_imputemean.Rd b/man/mlr_pipeops_imputemean.Rd
index e22dd44eb..2b800ab15 100644
--- a/man/mlr_pipeops_imputemean.Rd
+++ b/man/mlr_pipeops_imputemean.Rd
@@ -71,11 +71,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_imputemedian.Rd b/man/mlr_pipeops_imputemedian.Rd
index 4a001d67d..b89d8327f 100644
--- a/man/mlr_pipeops_imputemedian.Rd
+++ b/man/mlr_pipeops_imputemedian.Rd
@@ -71,11 +71,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_imputenewlvl.Rd b/man/mlr_pipeops_imputenewlvl.Rd
index 04313acfb..1b721bfd1 100644
--- a/man/mlr_pipeops_imputenewlvl.Rd
+++ b/man/mlr_pipeops_imputenewlvl.Rd
@@ -70,11 +70,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_imputesample.Rd b/man/mlr_pipeops_imputesample.Rd
index dcfb127c6..c2366d932 100644
--- a/man/mlr_pipeops_imputesample.Rd
+++ b/man/mlr_pipeops_imputesample.Rd
@@ -70,11 +70,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_kernelpca.Rd b/man/mlr_pipeops_kernelpca.Rd
index 21ff9e954..ddfcfd86f 100644
--- a/man/mlr_pipeops_kernelpca.Rd
+++ b/man/mlr_pipeops_kernelpca.Rd
@@ -85,11 +85,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_learner.Rd b/man/mlr_pipeops_learner.Rd
index e8e48ab37..6be255820 100644
--- a/man/mlr_pipeops_learner.Rd
+++ b/man/mlr_pipeops_learner.Rd
@@ -102,11 +102,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_missind.Rd b/man/mlr_pipeops_missind.Rd
index 81e0d5d64..28ffaabce 100644
--- a/man/mlr_pipeops_missind.Rd
+++ b/man/mlr_pipeops_missind.Rd
@@ -97,11 +97,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_modelmatrix.Rd b/man/mlr_pipeops_modelmatrix.Rd
index 667d4b2af..4044a25f7 100644
--- a/man/mlr_pipeops_modelmatrix.Rd
+++ b/man/mlr_pipeops_modelmatrix.Rd
@@ -77,11 +77,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_mutate.Rd b/man/mlr_pipeops_mutate.Rd
index c61b69399..f8431ed59 100644
--- a/man/mlr_pipeops_mutate.Rd
+++ b/man/mlr_pipeops_mutate.Rd
@@ -87,11 +87,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_nop.Rd b/man/mlr_pipeops_nop.Rd
index 9819472aa..95dce7cc8 100644
--- a/man/mlr_pipeops_nop.Rd
+++ b/man/mlr_pipeops_nop.Rd
@@ -79,11 +79,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_pca.Rd b/man/mlr_pipeops_pca.Rd
index 7486a2a5a..9894eea9e 100644
--- a/man/mlr_pipeops_pca.Rd
+++ b/man/mlr_pipeops_pca.Rd
@@ -88,11 +88,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_quantilebin.Rd b/man/mlr_pipeops_quantilebin.Rd
index 8fb87b063..0a27b7fc6 100644
--- a/man/mlr_pipeops_quantilebin.Rd
+++ b/man/mlr_pipeops_quantilebin.Rd
@@ -76,11 +76,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_regravg.Rd b/man/mlr_pipeops_regravg.Rd
index 52f0dfa82..805ce85b1 100644
--- a/man/mlr_pipeops_regravg.Rd
+++ b/man/mlr_pipeops_regravg.Rd
@@ -84,11 +84,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_removeconstants.Rd b/man/mlr_pipeops_removeconstants.Rd
index ede37e3ad..bacb84468 100644
--- a/man/mlr_pipeops_removeconstants.Rd
+++ b/man/mlr_pipeops_removeconstants.Rd
@@ -81,11 +81,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_scale.Rd b/man/mlr_pipeops_scale.Rd
index 8cc6fc10a..f28bb197b 100644
--- a/man/mlr_pipeops_scale.Rd
+++ b/man/mlr_pipeops_scale.Rd
@@ -89,11 +89,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_scalemaxabs.Rd b/man/mlr_pipeops_scalemaxabs.Rd
index 5c0a3ded3..afb8ea8cc 100644
--- a/man/mlr_pipeops_scalemaxabs.Rd
+++ b/man/mlr_pipeops_scalemaxabs.Rd
@@ -70,11 +70,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_scalerange.Rd b/man/mlr_pipeops_scalerange.Rd
index f2e7bb852..927c7c294 100644
--- a/man/mlr_pipeops_scalerange.Rd
+++ b/man/mlr_pipeops_scalerange.Rd
@@ -74,11 +74,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_select.Rd b/man/mlr_pipeops_select.Rd
index a8e2dc778..0bb250578 100644
--- a/man/mlr_pipeops_select.Rd
+++ b/man/mlr_pipeops_select.Rd
@@ -91,11 +91,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_smote.Rd b/man/mlr_pipeops_smote.Rd
index 1342596a3..73452abb8 100644
--- a/man/mlr_pipeops_smote.Rd
+++ b/man/mlr_pipeops_smote.Rd
@@ -93,11 +93,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_spatialsign.Rd b/man/mlr_pipeops_spatialsign.Rd
index 66452d64a..99281c9c5 100644
--- a/man/mlr_pipeops_spatialsign.Rd
+++ b/man/mlr_pipeops_spatialsign.Rd
@@ -70,11 +70,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_subsample.Rd b/man/mlr_pipeops_subsample.Rd
index 1adb7cc12..605da430c 100644
--- a/man/mlr_pipeops_subsample.Rd
+++ b/man/mlr_pipeops_subsample.Rd
@@ -89,11 +89,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_unbranch.Rd b/man/mlr_pipeops_unbranch.Rd
index a3405c64d..e357c8da1 100644
--- a/man/mlr_pipeops_unbranch.Rd
+++ b/man/mlr_pipeops_unbranch.Rd
@@ -82,11 +82,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/man/mlr_pipeops_yeojohnson.Rd b/man/mlr_pipeops_yeojohnson.Rd
index 158101398..045e9fe20 100644
--- a/man/mlr_pipeops_yeojohnson.Rd
+++ b/man/mlr_pipeops_yeojohnson.Rd
@@ -85,11 +85,13 @@ Other PipeOps: \code{\link{PipeOpEnsemble}},
   \code{\link{mlr_pipeops_classbalancing}},
   \code{\link{mlr_pipeops_classifavg}},
   \code{\link{mlr_pipeops_colapply}},
+  \code{\link{mlr_pipeops_collapsefactors}},
   \code{\link{mlr_pipeops_copy}},
   \code{\link{mlr_pipeops_encodelmer}},
   \code{\link{mlr_pipeops_encode}},
   \code{\link{mlr_pipeops_featureunion}},
   \code{\link{mlr_pipeops_filter}},
+  \code{\link{mlr_pipeops_fixfactors}},
   \code{\link{mlr_pipeops_histbin}},
   \code{\link{mlr_pipeops_ica}},
   \code{\link{mlr_pipeops_imputehist}},
diff --git a/tests/testthat/test_pipeop_fixfactors.R b/tests/testthat/test_pipeop_fixfactors.R
new file mode 100644
index 000000000..b67001a2e
--- /dev/null
+++ b/tests/testthat/test_pipeop_fixfactors.R
@@ -0,0 +1,108 @@
+context("PipeOpFixFactors")
+
+test_that("PipeOpFixFactors", {
+  task = mlr_tasks$get("boston_housing")
+
+  chaslevels = task$levels()$chas
+  townlevels = task$levels()$town
+
+  expect_datapreproc_pipeop_class(PipeOpFixFactors, task = task)
+
+  expect_datapreproc_pipeop_class(PipeOpFixFactors, task = mlr_tasks$get("iris"))
+
+  op = PipeOpFixFactors$new()
+  expect_pipeop(op)
+
+  nt = train_pipeop(op, inputs = list(task))[[1L]]
+  fn = nt$feature_names
+
+  # factor cols are removed
+  expect_true(all(c("chas", "town") %in% fn))
+  expect_set_equal(nt$levels()$chas, c("0", "1"))
+
+  nt = op$train(list(task$clone()$filter(1)))[[1]]
+
+  expect_equal(nt$levels()$chas, "0")
+  expect_equal(nt$levels()$town, "Nahant")
+  expect_equal(length(nt$levels()), 2)
+
+  nt = op$predict(list(task))[[1]]
+
+  expect_equal(nt$levels()$chas, "0")
+  expect_equal(nt$levels()$town, "Nahant")
+  expect_equal(length(nt$levels()), 2)
+
+  expect_equal(levels(nt$data()$chas), "0")
+  expect_equal(which(task$data()$chas == "1"), which(is.na(nt$data()$chas)))
+
+  nt = op$train(list(task$clone()$filter(1:2)))[[1]]
+
+  expect_equal(nt$levels()$chas, "0")
+  expect_set_equal(nt$levels()$town, c("Nahant", "Swampscott"))
+  expect_equal(length(nt$levels()), 2)
+
+  nt = op$predict(list(task))[[1]]
+  expect_equal(nt$levels()$chas, "0")
+  expect_set_equal(nt$levels()$town, c("Nahant", "Swampscott"))
+  expect_equal(length(nt$levels()), 2)
+
+  dattrain = data.table(
+    a = factor(c("a", "b", "c", NA), levels = letters),
+    b = ordered(c("a", "b", "c", NA)),
+    target = 1:4)
+
+  tasktrain = TaskRegr$new("train", dattrain, "target")
+
+  dattest = data.table(
+    a = factor(c("a", "b", "c", "d")),
+    b = ordered(c("a", "b", "c", "d"), levels = letters[10:1]),
+    target = 1:4)
+
+  tasktest = TaskRegr$new("train", dattest, "target")
+
+  op$param_set$values$droplevels = TRUE
+
+  opt = op$train(list(tasktrain))[[1]]
+
+  expect_equal(opt$levels(), list(a = letters[1:3], b = letters[1:3]))
+  expect_equal(levels(opt$data()$a), letters[1:3])
+  expect_equal(levels(opt$data()$b), letters[1:3])
+  expect_true(is.ordered(opt$data()$b))
+  expect_false(is.ordered(opt$data()$a))
+
+  opt = op$predict(list(tasktest))[[1]]
+
+  expect_equal(opt$levels(), list(a = letters[1:3], b = letters[1:3]))
+  expect_equal(levels(opt$data()$a), letters[1:3])
+  expect_equal(levels(opt$data()$b), letters[1:3])
+  expect_true(is.ordered(opt$data()$b))
+  expect_false(is.ordered(opt$data()$a))
+  expect_equal(opt$data()$a, factor(c("a", "b", "c", NA), levels = letters[1:3]))
+  expect_equal(opt$data()$b, ordered(c("a", "b", "c", NA), levels = letters[1:3]))
+
+  expect_equal(op$state$levels, list(a = letters[1:3], b = letters[1:3]))
+
+  op$param_set$values$droplevels = FALSE
+
+  opt = op$train(list(tasktrain))[[1]]
+
+  expect_equal(opt$levels(), list(a = letters, b = letters[1:3]))
+  expect_equal(levels(opt$data()$a), letters)
+  expect_equal(levels(opt$data()$b), letters[1:3])
+  expect_true(is.ordered(opt$data()$b))
+  expect_false(is.ordered(opt$data()$a))
+
+  opt = op$predict(list(tasktest))[[1]]
+
+  expect_equal(opt$levels(), list(a = letters, b = letters[1:3]))
+  expect_equal(levels(opt$data()$a), letters)
+  expect_equal(levels(opt$data()$b), letters[1:3])
+  expect_true(is.ordered(opt$data()$b))
+  expect_false(is.ordered(opt$data()$a))
+  expect_equal(opt$data()$a, factor(c("a", "b", "c", "d"), levels = letters))
+  expect_equal(opt$data()$b, ordered(c("a", "b", "c", NA), levels = letters[1:3]))
+
+  expect_equal(op$state$levels, list(a = letters, b = letters[1:3]))
+
+})
+