I am graphing longitudinal data from three time points. I'd like to draw a
solid line from point 1 to point 2, and then a dashed line from point 2 to
point 3. It works if I do it in two steps:

> first.vector <- c(mean(year1$variable1), mean(year2$variable1))
> second.vector <- c(NA, mean(year2$variable1), mean(year3$variable1))
> plot(first.vector, type="b", xlim=c(1,3))
> lines(second.vector, type="b", lty=2)

It's clunky, though, and I have a bunch of these to do. Can I streamline it?

TIA.

Jamie

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