[R] adding lines to stripchart

[Chuck Cleland]

James Root wrote:
> I have two points of collection across 20 subjects (pre and post for each),
> so 20 pairs of data points.  I would like to plot the actual raw data points
> for each subject for both pre and post and connect lines between these two
> points (20 in all) to depict real change between the two timepoints.
> 
> I have tried using stripchart which adequately plots the two lines of
> subject data points.  Attempting to use segments however has been
> difficult.  It seems that the segments command gives too many coordiate
> points - so where segments has:
> 
> x0, y0, x1, y1
> 
> I really only have two coordinates for each point -
> 
> pre to post
> 
> I am sure that I am misusing the command but not sure if I should continue
> to try with segments or if there is another command that would be more
> appropriate.
> 
> As always, thanks for any help.

  Here is how you might use segments() and stripchart():

df <- data.frame(pre = runif(20), post = runif(20))

stripchart(x = list(df$pre, df$post), vertical=TRUE,
group.names=c("Pre","Post"))

for(i in 1:nrow(df)){segments(1, df$pre[i], 2, df$post[i])}

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-- 
Chuck Cleland, Ph.D.
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