how to get a line plot before/after treatment

Dear R help-list reader,

I would like to generate a plot which compares to states in a patient 
treatment, before and after. for this reason I have generated a vector
before<-c(1,30,23,40)
and
after<-c(20,10,20,60)
the first element in "before" corresponds to the first element in "after".
I would like and generate a dotplot with
before and after as x-scale, the elements of "before" and "after" on 
the y-scale and the corresponding elements connected with a line.

However, so far I couldn't figure out how to do this in R. If anyone 
as a suggestion, please let me know

Many thanks

Frank

Dr. Mattes,

How about this, using interaction.plot() in package nlme (I am presuming
that each pair of measures is an independent pairing). It takes a bit to
get the data in the proper structure, but the plotting is then easy:


before <- c(1,30,23,40)
after <- c(20,10,20,60)

# Create a new dataframe with columns:
# 'score', 'when' and 'unit'
# 'when' and 'unit' are set to factors

before.new <- data.frame(score = before, when = "Before", 
                         unit = factor(1:4))

after.new <- data.frame(score = after, when = "After", 
                        unit = factor(1:4))

df.new <- rbind(before.new, after.new)

#display df.new to see the structure
df.new

# load nlme
library(nlme)

#attach the dataframe to call variables directly
attach(df.new)

#create plot
interaction.plot(when, unit, score, ylab = "Score", xlab = "When", 
                 col = rainbow(4))

# detach df.new to clean up
detach(df.new)



See ?interaction.plot for more information. This is a simple example of
the function which can handle repeated measures (the default y axis is
the means of scores) and multiple x-axis factors (for example if you had
before, 1 wk after and 2 wks after).

HTH,

Marc Schwartz