[R] dotplot/Dotplot: connecting points within factor level across time

[Benjamin Tyner]

For each level of the factor in dotplot, I have time points I'd like to 
connect with a line. In the example below, 'x' represents a starting 
time and 'd' a duration, and I wish to connect 'x' to 'x+d'. Ordinarily 
I would use Dotplot from hmisc for this, but I have not been able to 
find a time class that Dotplot will allow. I can get lattice dotplot to 
put the points up, but I've not figured out how to connect them. Any 
suggestions?

require(lattice)
z<-data.frame(y=factor(letters),
              x=structure(1:26,class=c("POSIXt","POSIXct"),tzone=""),
              d=runif(26))

# this puts the points, but does not connect them
p<-dotplot(y~x+I(x+d),
           data=z,
           scales=list(x=list(format="%M:%S"))
           )

zh<-z
zh$x<-as.numeric(zh$x)
require(hmisc)
# this connects them, but at the expense of the time info
ph<-Dotplot(y~Cbind(x,x,x+d),
            data=zh,
            pch=" ")



Thanks,
Ben