R语言

mytiantian

Introduction
R is a system for statistical computation and graphics. It provides, among other things, a programming
language, high level graphics, interfaces to other languages and debugging facilities.
This manual details and defines the R language.
The R language is a dialect of S which was designed in the 1980s and has been in widespread
use in the statistical community since. Its principal designer, John M. Chambers, was awarded
the 1998 ACM Software Systems Award for S.
The language syntax has a superficial similarity with C, but the semantics are of the FPL
(functional programming language) variety with stronger affinities with Lisp and APL. In particular,
it allows “computing on the language”, which in turn makes it possible to write functions
that take expressions as input, something that is often useful for statistical modeling and graphics.
It is possible to get quite far using R interactively, executing simple expressions from the
command line. Some users may never need to go beyond that level, others will want to write
their own functions either in an ad hoc fashion to systematize repetitive work or with the
perspective of writing add-on packages for new functionality.
The purpose of this manual is to document the language per se. That is, the objects that it
works on, and the details of the expression evaluation process, which are useful to know when
programming R functions. Major subsystems for specific tasks, such as graphics, are only briefly
described in this manual and will be documented separately.
Although much of the text will equally apply to S, there are also some substantial differences,
and in order not to confuse the issue we shall concentrate on describing R.
The design of the language contains a number of fine points and common pitfalls which may
surprise the user. Most of these are due to consistency considerations at a deeper level, as we
shall explain. There are also a number of useful shortcuts and idioms, which allow the user
to express quite complicated operations succinctly. Many of these become natural once one is
familiar with the underlying concepts. In some cases, there are multiple ways of performing a
task, but some of the techniques will rely on the language implementation, and others work at
a higher level of abstraction. In such cases we shall indicate the preferred usage.
Some familiarity with R is assumed. This is not an introduction to R but rather a programmers’
reference manual. Other manuals provide complementary information: in particular
section “Preface” in R Introduction provides an introduction to R and section “System and
foreign language interfaces” in Writing R Extensions details how to extend R using compiled
code.