#--Read in data file:
file <- "http://www.sr.bham.ac.uk/~ajrs/papers/sanderson09/sanderson09_table2.txt"
a <- read.table(file, header=TRUE, sep="|") 

#--Specfify output graphics device:
pdf(file="simple_dotplot.pdf", width=9, height=6)

#--Load extra library for plotting:
require(lattice)

#--Change factor level names to be more informative:
levels(a$cctype) <- c("Cool core", "Non-cool core")	# cool core status
levels(a$det) <- paste("ACIS", sep="-", levels(a$det))	# detector used

#--Use "+" and filled square instead of "o" for plot symbols:
trellis.par.set(superpose.symbol=list(pch=c(3,15)))

#--Create custom character string comprising the cluster name with the
#   observation identifier in brackets:
a$mystr <- with(a, paste(nedname, " (", obsid, ")", sep=""))

#--Create dot plot with clusters ordered by increasing redshift:
# NB "alternating=1" puts the X-axis labels on the bottom axes in all panels
#    "columns=2" creates side-by-side labels in the plot key (legend)
dotplot(reorder(mystr, z) ~ z | det, data=a, groups=cctype, 
        auto.key=list(columns=2), scale=list(alternating=1),
        xlab="Galaxy cluster redshift"
       )

#--Close plotting device:
dev.off()