Abstract
This article develops a generalization of the scatterplot matrix based on the recognition that most datasets include both categorical and quantitative information. Traditional grids of scatterplots often obscure important features of the data when one or more variables are categorical but coded as numerical. The generalized pairs plot offers a range of displays of paired combinations of categorical and quantitative variables. A mosaic plot, fluctuation diagram, or faceted bar chart may be used to display two categorical variables. A side-by-side boxplot, stripplot, faceted histogram, or density plot helps visualize a categorical and a quantitative variable. A traditional scatterplot is suitable for displaying a pair of numerical variables, but options also support density contours or annotating summary statistics such as the correlation and number of missing values, for example. By combining these, the generalized pairs plot may help to reveal structure in multivariate data that otherwise might go unnoticed in the process of exploratory data analysis. Two different R packages provide implementations of the generalized pairs plot, gpairs and GGally. Supplementary materials for this article are available online on the journal web site.
ACKNOWLEDGMENTS
The authors thank John Hartigan, Antony Unwin, and many students for advice and testing of these graphical displays. This work was partially supported by an unrestricted fellowship from Novartis, and by National Science Research grant DMS0706949.
Additional information
Notes on contributors
John W. Emerson
John W. Emerson is at the Department of Statistics, Yale University, New Haven, CT 06520 (E-mail: [email protected]). Walton A. Green is at the Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138. Barret Schloerke is at the Department of Statistics, Iowa State University, Ames, IA 50011. Jason Crowley is at the Department of Statistics, Iowa State University, Ames, IA 50011. Dianne Cook is at the Department of Statistics, Iowa State University, Ames, IA 50011. Heike Hofmann is at the Department of Statistics, Iowa State University, Ames, IA 50011. Hadley Wickham is at the Department of Statistics, Rice University, Houston, TX 77251.
Walton A. Green
John W. Emerson is at the Department of Statistics, Yale University, New Haven, CT 06520 (E-mail: [email protected]). Walton A. Green is at the Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138. Barret Schloerke is at the Department of Statistics, Iowa State University, Ames, IA 50011. Jason Crowley is at the Department of Statistics, Iowa State University, Ames, IA 50011. Dianne Cook is at the Department of Statistics, Iowa State University, Ames, IA 50011. Heike Hofmann is at the Department of Statistics, Iowa State University, Ames, IA 50011. Hadley Wickham is at the Department of Statistics, Rice University, Houston, TX 77251.
Barret Schloerke
John W. Emerson is at the Department of Statistics, Yale University, New Haven, CT 06520 (E-mail: [email protected]). Walton A. Green is at the Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138. Barret Schloerke is at the Department of Statistics, Iowa State University, Ames, IA 50011. Jason Crowley is at the Department of Statistics, Iowa State University, Ames, IA 50011. Dianne Cook is at the Department of Statistics, Iowa State University, Ames, IA 50011. Heike Hofmann is at the Department of Statistics, Iowa State University, Ames, IA 50011. Hadley Wickham is at the Department of Statistics, Rice University, Houston, TX 77251.
Jason Crowley
John W. Emerson is at the Department of Statistics, Yale University, New Haven, CT 06520 (E-mail: [email protected]). Walton A. Green is at the Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138. Barret Schloerke is at the Department of Statistics, Iowa State University, Ames, IA 50011. Jason Crowley is at the Department of Statistics, Iowa State University, Ames, IA 50011. Dianne Cook is at the Department of Statistics, Iowa State University, Ames, IA 50011. Heike Hofmann is at the Department of Statistics, Iowa State University, Ames, IA 50011. Hadley Wickham is at the Department of Statistics, Rice University, Houston, TX 77251.
Dianne Cook
John W. Emerson is at the Department of Statistics, Yale University, New Haven, CT 06520 (E-mail: [email protected]). Walton A. Green is at the Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138. Barret Schloerke is at the Department of Statistics, Iowa State University, Ames, IA 50011. Jason Crowley is at the Department of Statistics, Iowa State University, Ames, IA 50011. Dianne Cook is at the Department of Statistics, Iowa State University, Ames, IA 50011. Heike Hofmann is at the Department of Statistics, Iowa State University, Ames, IA 50011. Hadley Wickham is at the Department of Statistics, Rice University, Houston, TX 77251.
Heike Hofmann
John W. Emerson is at the Department of Statistics, Yale University, New Haven, CT 06520 (E-mail: [email protected]). Walton A. Green is at the Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138. Barret Schloerke is at the Department of Statistics, Iowa State University, Ames, IA 50011. Jason Crowley is at the Department of Statistics, Iowa State University, Ames, IA 50011. Dianne Cook is at the Department of Statistics, Iowa State University, Ames, IA 50011. Heike Hofmann is at the Department of Statistics, Iowa State University, Ames, IA 50011. Hadley Wickham is at the Department of Statistics, Rice University, Houston, TX 77251.
Hadley Wickham
John W. Emerson is at the Department of Statistics, Yale University, New Haven, CT 06520 (E-mail: [email protected]). Walton A. Green is at the Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138. Barret Schloerke is at the Department of Statistics, Iowa State University, Ames, IA 50011. Jason Crowley is at the Department of Statistics, Iowa State University, Ames, IA 50011. Dianne Cook is at the Department of Statistics, Iowa State University, Ames, IA 50011. Heike Hofmann is at the Department of Statistics, Iowa State University, Ames, IA 50011. Hadley Wickham is at the Department of Statistics, Rice University, Houston, TX 77251.