[R] drawing a line that shifts from solid to broken

[David Winsemius]

On Jan 30, 2010, at 10:33 AM, Jamie Smith wrote:

> 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))

Those don't look like adequate descriptions of a point to point graph  
element.

>> 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?

?segments  #takes vector arguments for x0, y0, x1, y1, and also for  
line type.

You would make the x1 and y1 vectors "offset" from x0 and y0 if you  
wanted the segments continuous.

-- 

David Winsemius, MD
Heritage Laboratories
West Hartford, CT