ABSTRACT
Most data from surveys and experiments include a mix of numeric values and text ids, and possibly also dates and times. Data sets are collections of heterogeneous values. Such values are stored in lists and data frames. These objects and how to operate on them are described in this chapter. Data frequently need to be inspected, aggregated or summarized, reshaped, split and combined. Data sets can be saved from R into files and read back into R from these files.
