a +1 shift overlaying lines/points on a boxplot (PR#398)

[Peter Dalgaard BSA]

acuster@nature.berkeley.edu writes:

> Full_Name: Adrian Custer
> Version: 0.90.0
> OS: Linux on Thinkpad (pentium) and desktop (K6)
> Submission from: (NULL) (128.32.251.234)
> 
> 
> When I create a boxplot, and then try to overlay a lowess fit or just the
> points, 
> the points do not appear in the highest level and the lowess curve does not
> reach 
> the highest level. However, if I add one to each of the models, the problem is
> solved.
> I tried this on two different machines, a laptop and a desktop both running 
> Gnu/linux+gnome. If you can't reproduce this please let me know.  -adrian
> 
> > a
>   [1]  0.629 -0.584  0.132 -0.012 -0.813 -0.291 -0.813 -0.291 -0.584 -0.164
...
> [291]  0.505  0.254 -0.188 -0.306  0.387  0.099  0.012  0.659  0.179  0.099
> > b
>   [1] 4 0 0 3 0 3 4 4 4 0 4 0 4 2 0 4 0 0 4 0 2 3 1 3 3 4 4 3 3 4 4 4 2 3 3 0 3
>  [38] 0 4 3 3 2 4 3 3 4 4 1 0 0 4 0 0 3 0 3 4 4 4 0 4 0 4 2 0 4 0 0 4 0 2 3 1 3
.....
> [297] 4 1 0 0
> > boxplot(a~b)
> > lines(lowess(a~b))
> > points(a~b)
> > boxplot(a~b)
> > lines(lowess(a~b+1))
> > points(a~b+1)
> > 
> 
> Thanks for your consideration and thanks a million for all the work. R is a
> pleasure 
> to work with. 

Boxplot expects a *factor* as the grouping criterion. The x axis
labels are the group names, not x coordinates (i.e. it might as well
be "married, unmarried, divorced" as "0, 1, 2."), and since factors
are internally coded as 1:nlevels, that's the value used for the
actual coordinate system.

Passing a numeric vector gets it converted to a factor before use, so
things are as you should expect. Except possibly for two issues:

a) should one really do the numeric->factor conversion without a
warning message?

b) perhaps boxplot could use an at= argument saying "plot boxes here"
since the current version wouldn't be able to deal with
non-equidistant groups. 

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907
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