Hammock Plots: Visualizing Categorical and Numerical Variables

I discuss the hammock plot for visualizing categorical or mixed categorical/numeric data. Hammock plots can be viewed as a generalization of parallel coordinate plots where the lines are replaced by boxes (or plotting elements) and the width of the boxes is proportional to the number of observations they represent. The article also introduces a modification to the hammock plot to avoid what Hoffman et al. termed the reverse line width illusion. Further, I give an historical overview over hammock-type plots such as common angle, GPCP, parsets, and alluvial plots and discuss the type of boxes used to connect adjacent variables. Supplementary materials for this article are available online.