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axisTicks: Compute Pretty Axis Tick Scales

axisTicks

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.
`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 ‘<Rsrc>/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, 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]`.

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)

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

plot(2^(0:9), log = "y"); (pu <- par("usr"))
aX(2, print(ya <- axisTicks(pu[3:4], log = TRUE)))  # y axis