The Art of R Programming

Applying Functions to Data Frames

As with lists, you can use the lapply and sapply functions with data frames.

Using lapply() and sapply() on Data Frames

Keep in mind that data frames are special cases of lists, with the list components consisting of the data frame’s columns. Thus, if you call lapply() on a data frame with a specified function f(), then f() will be called on each of the frame’s columns, with the return values placed in a list.

For instance, with our previous example, we can use lapply as follows:

> d
  kids ages
1 Jack   12
2 Jill   10
> dl <- lapply(d,sort)
> dl
$kids
[1] "Jack" "Jill"

$ages
[1] 10 12

So, dl is a list consisting of two vectors, the sorted versions of kids and ages.

Note that dl is just a list, not a data frame. We could ...