New Approaches in Visualization of Categorical Data: R Package extracat

Alexander Pilhöfer, Antony Unwin

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The R package extracat provides two new graphical methods for displaying categorical data extending the concepts of multiple barcharts and parallel coordinates plots. The first method called rmb plot uses a crossover of mosaicplots and multiple barcharts to display the frequencies of a data table split up into conditional relative frequencies of one target variable and the absolute frequencies of the corresponding combinations of the remaining explanatory variables. It provides a well-structured representation of the data which is easy to interpret and allows precise comparisons. The graphic can additionally be used as a generalization of spineplots or with barcharts for the conditional relative frequencies. Several options, including ceiling censored zooming, residual shadings and a choice of color palettes, are provided. An interactive version based on the R package iWidgets is also presented. The second graphic cpcp uses the interactive parallel coordinates plots in the iplots package to visualize categorical data. Sequences of points are used to represent each of the variable categories, while ordering algorithms are applied to represent a hierarchical structure in the data and keep the arrangement clear. This interactive graphic is well-suited for exploratory analysis and allows a visual interpretation even for a higher number of variables and a mixture of categorical and numeric scales.

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