\Header{axis}{Add an Axis to a Plot}
\keyword{aplot}{axis}
\begin{Description}\relax
Adds an axis to the current plot, allowing the
specification of the side, position, labels, and other options.\end{Description}
\begin{Usage}
\begin{verbatim}
axis(side, at, labels = TRUE, tick = TRUE, line = 0,
     pos = NA, outer = FALSE, font = NA, vfont = NULL, ...)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{side}] an integer specifying which side of the plot the axis is
to be drawn on.
\item[\code{at}] the points at which tick-marks are to be drawn. Non-finite
(infinite, \code{NaN} or \code{NA}) values are omitted.
\item[\code{labels}] this can either be a logical value specifying whether
(numerical) annotations are to be made at the tickmarks, or a vector
of character strings to be placed at the tickpoints.
\item[\code{tick}] a logical value specifying whether tickmarks should be
drawn
\item[\code{line}] the number of lines into the margin which the axis will
be drawn.  This overrides the value of the graphical parameter
\code{mgp[3]}.  The relative placing of tickmarks and tick labels
is unchanged.
\item[\code{pos}] the coordinate at which the axis line is to be drawn.
this overrides the value of both \code{line} and \code{mgp[3]}.
\item[\code{outer}] a logical value indicating whether the axis should be
drawn in the outer plot margin, rather than the standard plot
margin.
\item[\code{font}] font for text.
\item[\code{vfont}] vector font for text.
\item[\code{...}] graphical parameters may also be passed as arguments to
this function.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
The axis line is drawn from the lowest to the highest value of
\code{at}, but will be clipped at the plot region. Only ticks which
are drawn from points within the plot region (up to a tolerance for
rounding error) are plotted, but the ticks and their labels may well
extend outside the plot region.\end{Details}
\begin{Value}
This function is invoked for its side effect, which is to add an axis
to an already existing plot.  The axis is placed as follows: 1=below,
2=left, 3=above and 4=right.\end{Value}
\begin{Examples}
\begin{ExampleCode}
plot(1:4, rnorm(4), axes=FALSE)
axis(1, 1:4, LETTERS[1:4])
axis(2)
box() #- to make it look "as usual"

plot(1:7, rnorm(7), type = 's', xaxt='n', col = 'red')
axis(1, 1:7, LETTERS[1:7], col.axis = 'blue')

\end{ExampleCode}
\end{Examples}

