4

LISTS

In contrast to a vector, in which all ele-

ments must be of the same mode, R’slist

structure can combine objects of different

types. For those familiar with Python, an R list

is similar to a Python dictionary or, for that matter, a

Perl hash. C programmers may find it similar to a C

struct. The list plays a central role in R, forming the

basis for data frames, object-oriented programming,

and so on.

In this chapter, we’ll cover how to create lists and how to work with

them. As with vectors and matrices, one common operation with lists is

indexing. List indexing is similar to vector and matrix indexing but with

some major differences. And like matrices, lists have an analog for the

apply()function. We’ll discuss these and other list topics, including ways

to take lists apart, which often comes in handy.

4.1 Creating Lists...............................................................

Technically, a list is a vector. Ordinary vectors—those of the type we’ve

been using so far in this book—are termedatomicvectors, since their