(R-lang.info)Introduction

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1 Introduction
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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 Note: (R-intro)Preface
provides an introduction to R and Note: (R-exts)System and foreign
language interfaces details how to extend R using compiled code.