calc_density            Internal helper to calculate the
                        (group-specific) density of a variable
capitalize_firstLetter
                        Internal function to capitalize the first
                        letter of a character
compute_marginalAPCeffects
                        Internal helper to compute marginal APC effects
                        and their confidence intervals
compute_xCoordinate     Internal helper to tilt the x-axis for the
                        hexamap plot
compute_yCoordinate     Internal helper to tilt the x-axis for the
                        hexamap plot
create_APCsummary       Create a summary table for multiple estimated
                        GAM models
create_groupVariable    Internal helper to create a group variable as
                        base for a density matrix
create_highlightDiagonalData
                        Internal helper to create a dataset for ggplot2
                        to highlight diagonals
create_modelSummary     Create model summary tables for multiple
                        estimated GAM models
create_oneAPCsummaryTable
                        Internal helper to create a summary table for
                        one estimated GAM model
drug_deaths             Drug deaths of white men in the United States
ensure_segmentsInPlotRange
                        Internal helper for gg_addReferenceLines to
                        keep diagonal lines in the plot range
extract_summary_linearEffects
                        Internal helper to extract summary of linear
                        effects in a gam model
get_plotGAMobject       Extract returned values of plot.gam() while
                        suppressing creation of the plot
gg_addReferenceLines    Internal helper to add reference lines in an
                        APC heatmap
gg_highlightDiagonals   Internal helper to add the diagonal
                        highlighting to a ggplot
plot_1Dsmooth           Plot 1D smooth effects for 'gam' models
plot_APCheatmap         Heatmap of an APC surface
plot_APChexamap         Hexamap of an APC surface
plot_density            Plot the density of one metric or categorical
                        variable
plot_densityMatrix      Create a matrix of density plots
plot_density_categorical
                        Internal helper to plot a categorical density
plot_density_metric     Internal helper to plot a metric density
plot_jointMarginalAPCeffects
                        Joint plot to compare the marginal APC effects
                        of multiple models
plot_linearEffects      Plot linear effects of a gam in an effect plot
plot_marginalAPCeffects
                        Plot of marginal APC effects based on an
                        estimated GAM model
plot_partialAPCeffects
                        Partial APC plots based on an estimated GAM
                        model
plot_variable           Distribution plot of one variable against one
                        APC dimension
travel                  Data from the German Reiseanalyse survey
