Compute Axis Tickmark Locations

Description

Compute pretty tickmark locations, the same way as R does internally. This is only non-trivial when log coordinates are active. By default, gives the at values which axis(side) would use.

Usage

axTicks(side, axp = NULL, usr = NULL, log = NULL, nintLog = NULL)

Arguments

Details

The axp, usr, and log arguments must be consistent as their default values (the par(..) results) are. If you specify all three (as non-NULL), the graphics environment is not used at all. Note that the meaning of axp differs significantly when log is TRUE; see the documentation on par(xaxp = .).

axTicks() can be used an R interface to the C function CreateAtVector() in ‘..../src/main/plot.c’ which is called by axis(side, *) when no argument at is specified. The delicate case, log = TRUE, now makes use of axisTicks (in package grDevices) unless nintLog = Inf which exists for back compatibility.

Value

numeric vector of coordinate values at which axis tickmarks can be drawn. By default, when only the first argument is specified, these values should be identical to those that axis(side) would use or has used. Note that the values are decreasing when usr is (“reverse axis” case).

See Also

axis, par. pretty uses the same algorithm (but independently of the graphics environment) and has more options. However it is not available for log = TRUE.

axisTicks() (package grDevices).

Examples

 plot(1:7, 10*21:27)
 axTicks(1)
 axTicks(2)
 stopifnot(identical(axTicks(1), axTicks(3)),
           identical(axTicks(2), axTicks(4)))

## Show how axTicks() and axis() correspond :
op <- par(mfrow = c(3, 1))
for(x in 9999 * c(1, 2, 8)) {
    plot(x, 9, log = "x")
    cat(formatC(par("xaxp"), width = 5),";", T <- axTicks(1),"\n")
    rug(T, col =  adjustcolor("red", 0.5), lwd = 4)
}
par(op)

x <- 9.9*10^(-3:10)
plot(x, 1:14, log = "x")
axTicks(1) # now length 5, in R <= 2.13.x gave the following
axTicks(1, nintLog = Inf) # rather too many

## An example using axTicks() without reference to an existing plot
## (copying R's internal procedures for setting axis ranges etc.),
## You do need to supply _all_ of axp, usr, log, nintLog
## standard logarithmic y axis labels
ylims <- c(0.2, 88)
get_axp <- function(x) 10^c(ceiling(x[1]), floor(x[2]))
## mimic par("yaxs") == "i"
usr.i <- log10(ylims)
(aT.i <- axTicks(side = 2, usr = usr.i,
                 axp = c(get_axp(usr.i), n = 3), log = TRUE, nintLog = 5))
## mimic (default) par("yaxs") == "r"
usr.r <- extendrange(r = log10(ylims), f = 0.04)
(aT.r <- axTicks(side = 2, usr = usr.r,
                 axp = c(get_axp(usr.r), 3), log = TRUE, nintLog = 5))

## Prove that we got it right :
plot(0:1, ylims, log = "y", yaxs = "i")
stopifnot(all.equal(aT.i, axTicks(side = 2)))

plot(0:1, ylims, log = "y", yaxs = "r")
stopifnot(all.equal(aT.r, axTicks(side = 2)))

Results

R version 3.3.1 (2016-06-21) -- "Bug in Your Hair"
Copyright (C) 2016 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)

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Type 'contributors()' for more information and
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Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.

> library(graphics)
> png(filename="/home/ddbj/snapshot/RGM3/R_rel/result/graphics/axTicks.Rd_%03d_medium.png", width=480, height=480)
> ### Name: axTicks
> ### Title: Compute Axis Tickmark Locations
> ### Aliases: axTicks
> ### Keywords: dplot
> 
> ### ** Examples
> 
>  plot(1:7, 10*21:27)
>  axTicks(1)
[1] 1 2 3 4 5 6 7
>  axTicks(2)
[1] 210 220 230 240 250 260 270
>  stopifnot(identical(axTicks(1), axTicks(3)),
+            identical(axTicks(2), axTicks(4)))
> 
> ## Show how axTicks() and axis() correspond :
> op <- par(mfrow = c(3, 1))
> for(x in 9999 * c(1, 2, 8)) {
+     plot(x, 9, log = "x")
+     cat(formatC(par("xaxp"), width = 5),";", T <- axTicks(1),"\n")
+     rug(T, col =  adjustcolor("red", 0.5), lwd = 4)
+ }
 1000 1e+05     3 ; 200 500 1000 2000 5000 10000 20000 50000 1e+05 2e+05 5e+05 
 1000 1e+06     2 ; 500 1000 5000 10000 50000 1e+05 5e+05 1e+06 
 1000 1e+07     1 ; 1000 10000 1e+05 1e+06 1e+07 
> par(op)
> 
> x <- 9.9*10^(-3:10)
> plot(x, 1:14, log = "x")
> axTicks(1) # now length 5, in R <= 2.13.x gave the following
[1] 1e-02 1e+01 1e+04 1e+07 1e+10
> axTicks(1, nintLog = Inf) # rather too many
 [1] 1e-02 1e-01 1e+00 1e+01 1e+02 1e+03 1e+04 1e+05 1e+06 1e+07 1e+08 1e+09
[13] 1e+10 1e+11
> 
> ## An example using axTicks() without reference to an existing plot
> ## (copying R's internal procedures for setting axis ranges etc.),
> ## You do need to supply _all_ of axp, usr, log, nintLog
> ## standard logarithmic y axis labels
> ylims <- c(0.2, 88)
> get_axp <- function(x) 10^c(ceiling(x[1]), floor(x[2]))
> ## mimic par("yaxs") == "i"
> usr.i <- log10(ylims)
> (aT.i <- axTicks(side = 2, usr = usr.i,
+                  axp = c(get_axp(usr.i), n = 3), log = TRUE, nintLog = 5))
[1]  0.2  0.5  1.0  2.0  5.0 10.0 20.0 50.0
> ## mimic (default) par("yaxs") == "r"
> usr.r <- extendrange(r = log10(ylims), f = 0.04)
> (aT.r <- axTicks(side = 2, usr = usr.r,
+                  axp = c(get_axp(usr.r), 3), log = TRUE, nintLog = 5))
[1]   0.2   0.5   1.0   2.0   5.0  10.0  20.0  50.0 100.0
> 
> ## Prove that we got it right :
> plot(0:1, ylims, log = "y", yaxs = "i")
> stopifnot(all.equal(aT.i, axTicks(side = 2)))
> 
> plot(0:1, ylims, log = "y", yaxs = "r")
> stopifnot(all.equal(aT.r, axTicks(side = 2)))
> 
> 
> 
> 
> 
> dev.off()
null device 
          1 
>