R help - Sep 2005 - horizontal lines on stripchart

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

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