Other Factor- and Table-Related Functions
R includes a number of other functions that are handy for working with tables and factors. We’ll discuss two of them here: aggregate() and cut().
Note
Hadley Wickham’s reshape package “lets you flexibly restructure and aggregate data using just two functions: melt and cast.” This package may take a while to learn, but it is extremely powerful. His plyr package is also quite versatile. You can download both packages from R’s CRAN repository. See Appendix B for more details about downloading and installing packages.
The aggregate() Function
The aggregate() function calls tapply() once for each variable in a group. For example, in the abalone data, we could find the median of each variable, broken down by gender, ...
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