diff --git a/R/boxwhisker-datamapping.R b/R/boxwhisker-datamapping.R
index e2928f8a..101a49d7 100644
--- a/R/boxwhisker-datamapping.R
+++ b/R/boxwhisker-datamapping.R
@@ -57,7 +57,7 @@ BoxWhiskerDataMapping <- R6::R6Class(
       if (isOfLength(self$x, 0)) {
         data$legendLabels <- factor("")
       }
-
+      
       # Transform names into functions for aggregation summary
       boxWhiskerLimitsFunctions <- sapply(self$boxWhiskerLimits, match.fun)
 
@@ -75,6 +75,9 @@ BoxWhiskerDataMapping <- R6::R6Class(
 
       # Dummy variable for aesthetics
       boxWhiskerLimits$legendLabels <- factor("")
+      if(!isOfLength(self$x, 0)){
+        boxWhiskerLimits[,self$x] <- as.factor(boxWhiskerLimits[,self$x])
+        }
 
       return(boxWhiskerLimits)
     },
@@ -89,7 +92,7 @@ BoxWhiskerDataMapping <- R6::R6Class(
       if (isOfLength(self$x, 0)) {
         data$legendLabels <- factor("")
       }
-
+      
       # Transform names into functions for aggregation summary
       outlierLimitsFunctions <- sapply(self$outlierLimits, match.fun)
 
@@ -120,6 +123,9 @@ BoxWhiskerDataMapping <- R6::R6Class(
 
       # Dummy variable for aesthetics
       outliers$legendLabels <- factor("")
+      if(!isOfLength(self$x, 0)){
+        outliers[,self$x] <- as.factor(outliers[,self$x])
+      }
 
       return(outliers)
     }
diff --git a/R/datamapping-xygroup.R b/R/datamapping-xygroup.R
index b3a59c30..c48ad17d 100644
--- a/R/datamapping-xygroup.R
+++ b/R/datamapping-xygroup.R
@@ -65,7 +65,7 @@ XYGDataMapping <- R6::R6Class(
 
       # All possible Groupings are listed in the enum LegendTypes
       for (groupType in LegendTypes) {
-        if (!is.null(self$groupMapping[[groupType]]$group)) {
+        if (isOfLength(self$groupMapping[[groupType]]$group, 0)) {next}
           grouping <- self$groupMapping[[groupType]]
 
           groupVariables <- grouping$group
@@ -76,15 +76,20 @@ XYGDataMapping <- R6::R6Class(
             groupVariables <- utils::head(groupVariables, -1)
           }
           validateMapping(groupVariables, data)
-          self$data[, grouping$label] <- grouping$getCaptions(data, metaData)
-          # Dummy variable for default aesthetics
-          # Will be used to define legend labels
-          self$data$legendLabels <- ifnotnull(
-            self$data$legendLabels,
-            paste(self$data$legendLabels, grouping$getCaptions(data, metaData), sep = "-"),
-            grouping$getCaptions(data, metaData)
-          )
-        }
+          # Enforce grouping variables to be factors
+          self$data[, grouping$label] <- as.factor(grouping$getCaptions(data, metaData))
+          
+          # Dummy variable for default aesthetics that will be used to define legend labels
+          legendLabels <- self$data$legendLabels %||% grouping$getCaptions(data, metaData)
+          
+          # Prevent duplication of legend if groupings are the same
+          if(all(as.character(legendLabels) == as.character(grouping$getCaptions(data, metaData)))){
+            self$data$legendLabels <- legendLabels
+            next
+          }
+          self$data$legendLabels <- as.factor(paste(as.character(self$data$legendLabels), 
+                                                    as.character(grouping$getCaptions(data, metaData)), 
+                                                    sep = "-"))
       }
 
       if (is.null(self$data$legendLabels)) {
diff --git a/R/tornado-datamapping.R b/R/tornado-datamapping.R
index c92cff9d..c53c34fe 100644
--- a/R/tornado-datamapping.R
+++ b/R/tornado-datamapping.R
@@ -46,6 +46,20 @@ TornadoDataMapping <- R6::R6Class(
 
       self$lines <- lines
       self$sorted <- sorted %||% TRUE
+    },
+    
+    #' @description Check that \code{data} variables include map variables
+    #' @param data data.frame to check
+    #' @param metaData list containing information on \code{data}
+    #' @return A data.frame with map and \code{defaultAes} variables.
+    #' Dummy variable \code{defaultAes} is necessary to allow further modification of plots.
+    checkMapData = function(data, metaData = NULL) {
+      mapData <- super$checkMapData(data, metaData)
+      # Enforce y to be a discrete variable preventing crashes from numerical values
+      if(!isOfLength(self$y, 0)){
+        mapData[,self$y] <- as.factor(mapData[,self$y])
+      }
+      return(mapData)
     }
   )
 )
diff --git a/man/TornadoDataMapping.Rd b/man/TornadoDataMapping.Rd
index 620de26d..6c2a6b02 100644
--- a/man/TornadoDataMapping.Rd
+++ b/man/TornadoDataMapping.Rd
@@ -22,13 +22,13 @@ R6 class for mapping \code{values}, \code{labels} to \code{data}
 \subsection{Public methods}{
 \itemize{
 \item \href{#method-new}{\code{TornadoDataMapping$new()}}
+\item \href{#method-checkMapData}{\code{TornadoDataMapping$checkMapData()}}
 \item \href{#method-clone}{\code{TornadoDataMapping$clone()}}
 }
 }
 \if{html}{
 \out{<details open ><summary>Inherited methods</summary>}
 \itemize{
-\item \out{<span class="pkg-link" data-pkg="tlf" data-topic="XYGDataMapping" data-id="checkMapData">}\href{../../tlf/html/XYGDataMapping.html#method-checkMapData}{\code{tlf::XYGDataMapping$checkMapData()}}\out{</span>}
 }
 \out{</details>}
 }
@@ -67,6 +67,29 @@ A new \code{TornadoDataMapping} object
 }
 }
 \if{html}{\out{<hr>}}
+\if{html}{\out{<a id="method-checkMapData"></a>}}
+\if{latex}{\out{\hypertarget{method-checkMapData}{}}}
+\subsection{Method \code{checkMapData()}}{
+Check that \code{data} variables include map variables
+\subsection{Usage}{
+\if{html}{\out{<div class="r">}}\preformatted{TornadoDataMapping$checkMapData(data, metaData = NULL)}\if{html}{\out{</div>}}
+}
+
+\subsection{Arguments}{
+\if{html}{\out{<div class="arguments">}}
+\describe{
+\item{\code{data}}{data.frame to check}
+
+\item{\code{metaData}}{list containing information on \code{data}}
+}
+\if{html}{\out{</div>}}
+}
+\subsection{Returns}{
+A data.frame with map and \code{defaultAes} variables.
+Dummy variable \code{defaultAes} is necessary to allow further modification of plots.
+}
+}
+\if{html}{\out{<hr>}}
 \if{html}{\out{<a id="method-clone"></a>}}
 \if{latex}{\out{\hypertarget{method-clone}{}}}
 \subsection{Method \code{clone()}}{