Create labels for the features

        NOTE: this code is duplicated from MultiFeatureVisualizer

def _create_labels_for_features(self, X):
        """
        Create labels for the features

        NOTE: this code is duplicated from MultiFeatureVisualizer
        """
        if self.labels is None:
            # Use column names if a dataframe
            if is_dataframe(X):
                self.features_ = np.array(X.columns)
            # Otherwise use the column index as the labels
            else:
                _, ncols = X.shape
                self.features_ = np.arange(0, ncols)
        else:
            self.features_ = np.array(self.labels)