axisTicks: 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.

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.

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

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.

Examples

Run this code

# NOT RUN {
##--- 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, n = 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

# }

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