R Programming By Example

Data frames

Now we turn to data frames, which are a lot like spreadsheets or database tables. In scientific contexts, experiments consist of individual observations (rows), each of which involves several different variables (columns). Often, these variables contain different data types, which would not be possible to store in matrices since they must contain a single data type. A data frame is a natural way to represent such heterogeneous tabular data. Every element within a column must be of the same type, but different elements within a row may be of different types, that's why we say that a data frame is a heterogeneous data structure.

Technically, a data frame is a list whose elements are equal-length vectors, and that's why it permits ...