\HeaderA{Comparison}{Relational Operators}{Comparison}
\aliasA{"!=}{Comparison}{"!=}
\aliasA{<}{Comparison}{<}
\aliasA{<=}{Comparison}{<=}
\aliasA{==}{Comparison}{==}
\aliasA{>}{Comparison}{>}
\aliasA{>=}{Comparison}{>=}
\keyword{logic}{Comparison}
\begin{Description}\relax
Binary operators which allow the comparison of values in atomic vectors.
\end{Description}
\begin{Usage}
\begin{verbatim}
x < y
x > y
x <= y
x >= y
x == y
x != y
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x, y}] atomic vectors, or other objects for which methods have
been written.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
The binary comparison operators are generic functions: methods can be
written for them individually or via the \code{\LinkA{Ops}{Ops}}) group generic
function.

Comparison of strings in character vectors is lexicographic within the
strings using the collating sequence of the locale in use: see
\code{\LinkA{locales}{locales}}.  The collating sequence of locales such as
\samp{en\_US} is normally different from \samp{C} (which should use
ASCII) and can be surprising.

At least one of \code{x} and \code{y} must be an atomic vector, but if
the other is a list \R{} attempts to coerce it to the type of the atomic
vector: this will succeed if the list is made up of elements of length
one that canbe coerced to the correct type.

If the two arguments are atomic vectors of different types, they are
both coerced to the first of character, complex, numeric, integer and
logical.
\end{Details}
\begin{Value}
A vector of logicals indicating the result of the element by element
comparison.  The elements of shorter vectors are recycled as
necessary.

Objects such as arrays or time-series can be compared this way
provided they are conformable.
\end{Value}
\begin{Note}\relax
Don't use \code{==} and \code{!=} for tests, such as in \code{if}
expressions, where you must get a single \code{TRUE} or
\code{FALSE}.  Unless you are absolutely sure that nothing unusual
can happen, you should use the \code{\LinkA{identical}{identical}} function
instead.

For numerical values, remember \code{==} and \code{!=} do not allow
for the finite representation of fractions, nor for rounding error.
Using \code{\LinkA{all.equal}{all.equal}} with \code{identical} is almost
always preferable.  See the examples.
\end{Note}
\begin{References}\relax
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
\emph{The New S Language}.
Wadsworth \& Brooks/Cole.
\end{References}
\begin{SeeAlso}\relax
\code{\LinkA{Syntax}{Syntax}} for operator precedence.
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
x <- rnorm(20)
x < 1
x[x > 0]

x1 <- 0.5 - 0.3
x2 <- 0.3 - 0.1
x1 == x2                           # FALSE on most machines
identical(all.equal(x1, x2), TRUE) # TRUE everywhere
\end{ExampleCode}
\end{Examples}

