The plyr package has functions that provide powerful and flexible data manipulation abilities. Functions have names in the style of aaply(), adply(), and so on, where the first letter of the name...

The plyr package has functions that provide powerful and flexible data manipulation abilities. Functions have names in the style of aaply(), adply(), and so on, where the first letter of the name indicates the class of object that will be used as input (for adply() it is a = array), and the second letter denotes the output class (for adply() it is d = data frame). In addition to array and data frame, note l = list. Try the following, and in each case explain the result: