axis
Add an Axis to a Plot
Adds an axis to the current plot, allowing the specification of the side, position, labels, and other options.
- Keywords
- aplot
Usage
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, …)Arguments
- side
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.
- at
the points at which tick-marks are to be drawn. Non-finite (infinite,
NaNorNA) values are omitted. By default (whenNULL) tickmark locations are computed, see ‘Details’ below.- labels
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,atshould also be supplied and of the same length. Iflabelsis of length zero after coercion, it has the same effect as supplyingTRUE.- tick
a logical value specifying whether tickmarks and an axis line should be drawn.
- line
the number of lines into the margin at which the axis line will be drawn, if not
NA.- pos
the coordinate at which the axis line is to be drawn: if not
NAthis overrides the value ofline.- outer
a logical value indicating whether the axis should be drawn in the outer plot margin, rather than the standard plot margin.
- font
font for text. Defaults to
par("font").- lty
line type for both the axis line and the tick marks.
- lwd, lwd.ticks
line widths for the axis line and the tick marks. Zero or negative values will suppress the line or ticks.
- col, col.ticks
colors for the axis line and the tick marks respectively.
col = NULLmeans to usepar("fg"), possibly specified inline, andcol.ticks = NULLmeans to use whatever colorcolresolved to.- hadj
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).- padj
adjustment for each tick label perpendicular to the reading direction. For labels parallel to the axes,
padj = 0means right or top alignment, andpadj = 1means left or bottom alignment. This can be a vector given a value for each string, and will be recycled as necessary.If
padjis not a finite value (the default), the value ofpar("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.axisandfont.axisfor axis annotation,mgpandxaxporyaxpfor positioning,tckortclfor tick mark length and direction,lasfor vertical/horizontal label orientation, orfginstead ofcol, andxpdfor clipping. Seeparon these.Parameters
xaxt(sides 1 and 3) andyaxt(sides 2 and 4) control if the axis is plotted at all.Note that
labwill partial match to argumentlabelsunless the latter is also supplied. (Since the default axes have already been set up byplot.window,labwill not be acted on byaxis.)
Details
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. 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.
Value
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.
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
See Also
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.
Examples
library(graphics)
# 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))
# }