axisTicks {grDevices}R Documentation

Compute Pretty Axis Tick Scales

Description

Compute pretty axis scales and tick mark locations, the same way as traditional R graphics do it. This is interesting particularly for log scale axes.

Usage

axisTicks(usr, log, axp = NULL, nint = 5)
.axisPars(usr, log = FALSE,  nintLog = 5)

Arguments

usr

numeric vector of length 2, with c(min, max) axis extents. Corresponds to traditional graphics' par("usr"), and hence for log = TRUE needs to use log10() transformed coordinates.

log

logical indicating if a log scale is (thought to be) in use.

axp

numeric vector of length 3, c(mi, ma, n.), with identical meaning to par("?axp") (where ? is x or y), namely “pretty” axis extents, and an integer code n..

nint, nintLog

positive integer value indicating (approximately) the desired number of intervals. nintLog is used only for the case log = TRUE.

Details

axisTicks(usr, *) calls .axisPars(usr, ..) to set axp when that is missing or NULL.

Apart from that, axisTicks() just calls the C function CreateAtVector() in ‘R/src/main/plot.c’ which is also called by the base graphics package function axis(side, *) when its argument at is not specified.

Since R 4.1.0, the underlying C CreateAtVector() has been tuned to provide a considerably more balanced (symmetric) set of tick locations.

Value

axisTicks() returns a numeric vector of potential axis tick locations in case of log=TRUE in the original scale, of length approximately nint+1.

.axisPars() returns a list with components

axp

numeric vector of length 2, c(min., max.), of pretty axis extents.

n

integer (code), with the same meaning as par("?axp")[3].

See Also

axTicks, axis, and par all from the graphics package.

Examples

##--- Demonstrating correspondence between graphics'
##--- axis() and the graphics-engine agnostic  axisTicks() :

require("graphics")
plot(10*(0:10)); (pu <- par("usr"))
aX <- function(side, at, ...)
    axis(side, at = at, labels = FALSE, lwd.ticks = 2, col.ticks = 2,
         tck = 0.05, ...)
aX(1, print(xa <- axisTicks(pu[1:2], log = FALSE)))  # x axis
aX(2, print(ya <- axisTicks(pu[3:4], log = FALSE)))  # y axis

axisTicks(pu[3:4], log = FALSE, nint = 10)


## --------------------  Log Scale  --------------------------------
x <- c(10, 1000)
#         _____
axisTicks(log10(x), log = TRUE) #  10 20 50 .... 1000

plot(10*(0:10), log = "y"); (pu <- par("usr")) # ... ...  0.96 2.04
aX(2, print(ya <- axisTicks(pu[3:4], log = TRUE)))  # 10 20 50 100 (y axis)

plot(2^(0:9), log = "y"); (pu <- par("usr")) # 
aX(2, print(ya <- axisTicks(pu[3:4], log = TRUE)))  # y axis
## 'usr' corresponds to log10(<range>) :
stopifnot(ya == axisTicks(log10(c(1, 512)), log=TRUE))
[Package grDevices version 4.5.0 Index]