[R] horizontal lines on stripchart

Uwe Ligges ligges at statistik.uni-dortmund.de
Sat Sep 17 14:05:48 CEST 2005

Iain Gallagher wrote:
> Hi.
> I would like to add a horizontal line to each column of data on a 
> stripchart (vertical=T) to indicate the mean(rather like the package 
> Prism does - for those that have used this) for each dataset. I presume 
> the best way to do this would be with "lines" but after much trying  / 
> playing about I can't figure it out. Can anyone help?
> Thanks
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Example adapted from ?stripchart:

with(OrchardSprays, {
     stripchart(decrease ~ treatment,
         main = "stripchart(Orchardsprays)", ylab = "decrease",
         vertical = TRUE)
     m <- tapply(decrease, treatment, mean)
     segments(1:nlevels(treatment)-0.25, m, 1:nlevels(treatment)+0.25, m)

Uwe Ligges

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