Adds an axis to the current plot, allowing the specification of the side, position, labels, and other options.
axis(side, at = NULL, labels = TRUE, tick = TRUE, line = NA,
pos = NA, outer = FALSE, font = NA, lty = "solid",
lwd = 1, lwd.ticks = lwd, col = NULL, col.ticks = NULL,
hadj = NA, padj = NA, …)an integer specifying which side of the plot the axis is to be drawn on. The axis is placed as follows: 1=below, 2=left, 3=above and 4=right.
the points at which tick-marks are to be drawn. Non-finite
(infinite, NaN or NA) values are omitted. By default
(when NULL) tickmark locations are computed, see
‘Details’ below.
this can either be a logical value specifying whether
(numerical) annotations are to be made at the tickmarks, or a
character or expression vector of labels to be placed at the
tickpoints. (Other objects are coerced by as.graphicsAnnot.)
If this is not logical, at should also be supplied and of the
same length. If labels is of length zero after coercion,
it has the same effect as supplying TRUE.
a logical value specifying whether tickmarks and an axis line should be drawn.
the number of lines into the margin at which the axis line
will be drawn, if not NA.
the coordinate at which the axis line is to be drawn:
if not NA this overrides the value of line.
a logical value indicating whether the axis should be drawn in the outer plot margin, rather than the standard plot margin.
font for text. Defaults to par("font").
line type for both the axis line and the tick marks.
line widths for the axis line and the tick marks. Zero or negative values will suppress the line or ticks.
colors for the axis line and the tick marks
respectively. col = NULL means to use par("fg"),
possibly specified inline, and col.ticks = NULL means to use
whatever color col resolved to.
adjustment (see par("adj")) for all labels
parallel (‘horizontal’) to the reading direction. If
this is not a finite value, the default is used (centring for
strings parallel to the axis, justification of the end nearest the
axis otherwise).
adjustment for each tick label perpendicular to the
reading direction. For labels parallel to the axes, padj = 0
means right or top alignment, and padj = 1 means left or bottom
alignment. This can be a vector given a value for each string, and
will be recycled as necessary.
If padj is not a finite value (the default), the value of
par("las") determines the adjustment. For strings plotted
perpendicular to the axis the default is to centre the string.
other graphical parameters may also be passed as
arguments to this function, particularly, cex.axis,
col.axis and font.axis for axis annotation, mgp
and xaxp or yaxp for positioning, tck or
tcl for tick mark length and direction, las for
vertical/horizontal label orientation, or fg instead of
col, and xpd for clipping. See par on these.
Parameters xaxt (sides 1 and 3) and yaxt (sides 2 and
4) control if the axis is plotted at all.
Note that lab will partial match to argument
labels unless the latter is also supplied. (Since the
default axes have already been set up by plot.window,
lab will not be acted on by axis.)
The numeric locations on the axis scale at which tick marks were drawn when the plot was first drawn (see ‘Details’).
This function is usually invoked for its side effect, which is to add an axis to an already existing plot.
The axis line is drawn from the lowest to the highest value of
at, but will be clipped at the plot region. By default, 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. Use xpd = TRUE
or xpd = NA to allow axes to extend further.
When at = NULL, pretty tick mark locations are computed internally
(the same way axTicks(side) would) from
par("xaxp") or "yaxp" and
par("xlog") (or "ylog"). Note that these
locations may change if an on-screen plot is resized (for example, if
the plot argument asp (see plot.window) is set.)
If labels is not specified, the numeric values supplied or
calculated for at are converted to character strings as if they
were a numeric vector printed by print.default(digits = 7).
The code tries hard not to draw overlapping tick labels, and so will
omit labels where they would abut or overlap previously drawn labels.
Currently, this applies only for labels written parallel to the
axis direction, hence not for e.g., las = 2. It is planned to
extend this, so perpendicular labels would also not overlap.
This can result in, for example, every other tick being labelled.
(The ticks are drawn left to right or bottom to top, and space at
least the size of an ‘m’ is left between labels.)
If either line or pos is set, they (rather than
par("mgp")[3]) determine the position of the axis line and tick
marks, and the tick labels are placed par("mgp")[2] further
lines into (or towards for pos) the margin.
Several of the graphics parameters affect the way axes are drawn. The
vertical (for sides 1 and 3) positions of the axis and the tick labels
are controlled by mgp[2:3] and mex, the size and
direction of the ticks is controlled by tck and tcl and
the appearance of the tick labels by cex.axis, col.axis
and font.axis with orientation controlled by las (but
not srt, unlike S which uses srt if at is
supplied and las if it is not). Note that adj is not
supported and labels are always centered. See par for details.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
Axis for a generic interface.
axTicks returns the axis tick locations
corresponding to at = NULL; pretty is more flexible
for computing pretty tick coordinates and does not depend on
(nor adapt to) the coordinate system in use.
Several graphics parameters affecting the appearance are documented
in par.
# NOT RUN {
require(stats) # for rnorm
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), main = "axis() examples",
type = "s", xaxt = "n", frame = FALSE, col = "red")
axis(1, 1:7, LETTERS[1:7], col.axis = "blue")
# unusual options:
axis(4, col = "violet", col.axis = "dark violet", lwd = 2)
axis(3, col = "gold", lty = 2, lwd = 0.5)
# one way to have a custom x axis
plot(1:10, xaxt = "n")
axis(1, xaxp = c(2, 9, 7))
# }
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