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Data Frames

A data frame (or data set) is a special type of list in which each variable is constrained to have the same number of observations. A data frame may contain variables of different types (numeric, integer, logical, character, and factor), so long as each variable has the same number of observations.

Thus, a data frame can use both matrix commands and list commands to manipulate variables and observations.

> dat[1:10,]         # Extracts observations 1-10 and all associated variables  
> dat[dat$grp == 1,] # Extracts all observations that belong to group 1 
> group <- dat$grp   # Saves the variable `grp' as a vector `group' in
                     #   the workspace, not in the data frame
> var4 <- dat[[4]]   # Saves the 4th variable as a `var4' in the workspace

For a comprehensive introduction to data frames and recoding data, see Section .