Displaying minor logarithmic ticks in x-axis in R
There is a function minor.tick
in the package Hmisc
, but that one deals poorly with logarithmical scales. I use the following function for getting minor ticks that follow the logarithmical scale. ax
is the axis you use it on (same as for the function axis
), n
is the number of minor ticks (default to 9), t.ratio
is the ratio between the major and the minor ticks, and with ...
you can pass extra parameters to axis
edit : Nice idea in the comments, so I edited my function. There are two extra parameters, mn
and mx
for the minimum and the maximum on the logarithmic scale (mn=0
thus means the minimum is 10^0 or 1 !)
The function:
minor.ticks.axis <- function(ax,n,t.ratio=0.5,mn,mx,...){ lims <- par("usr") if(ax %in%c(1,3)) lims <- lims[1:2] else lims[3:4] major.ticks <- pretty(lims,n=5) if(missing(mn)) mn <- min(major.ticks) if(missing(mx)) mx <- max(major.ticks) major.ticks <- major.ticks[major.ticks >= mn & major.ticks <= mx] labels <- sapply(major.ticks,function(i) as.expression(bquote(10^ .(i))) ) axis(ax,at=major.ticks,labels=labels,...) n <- n+2 minors <- log10(pretty(10^major.ticks[1:2],n))-major.ticks[1] minors <- minors[-c(1,n)] minor.ticks = c(outer(minors,major.ticks,`+`)) minor.ticks <- minor.ticks[minor.ticks > mn & minor.ticks < mx] axis(ax,at=minor.ticks,tcl=par("tcl")*t.ratio,labels=FALSE)}
This can be applied as follows :
x <- 10^(0:8)y <- 1:9plot(log10(x),y,xaxt="n",xlab="x",xlim=c(0,9))minor.ticks.axis(1,9,mn=0,mx=8)
Gives :
Here is a simple function to to this:
log10.axis <- function(side, at, ...) { at.minor <- log10(outer(1:9, 10^(min(at):max(at)))) lab <- sapply(at, function(i) as.expression(bquote(10^ .(i)))) axis(side=side, at=at.minor, labels=NA, tcl=par("tcl")*0.5, ...) axis(side=side, at=at, labels=lab, ...)}
Here is an example:
x <- exp(rnorm(200, 5))hist(log(x), 20, xaxt="n", xlim=c(0, 8))log10.axis(1, at=seq(0, 8, 2))