[R] Equal vertical spaced labels on plot with log="y"

[Jim Lemon]

Daniel Brewer wrote:
> Hello,
> 
> I have a series of labels that I want to place on a plot with a log
> scale y axis.  I want these labels to be equally spaced vertically as
> seen on the plot.
> 
> I have been trying this:
> 
> ylab <- 160 - log2(1:length(labels))
> 
> but that does not seem to work (where 160 is basically the top of the plot).
> 
Hi Daniel,
The method I use is to get the "real" coordinates on the plot:

xylim<-par("usr")

turn off the log transformation:

par(ylog=FALSE)

say I have three labels that I want to space:

ypos<-xylim[3]+(xylim[4]-xylim[3])*c(0.2,0.5,0.8)
text(xpos,ypos,c("first","second","third"))
# turn the y log transformation on again if necessary
par(ylog=TRUE)

I assume you can work out xpos for yourself.

Jim