[R] controlling the x axis of boxplots

[Rich FitzJohn]

Hi Chris,

You can get the desired effect by using the "at" argument to boxplot,
and by setting up the plot dimensions manually.

men <- data.frame(grp=rep(letters[c(1, 2, 4, 6)], each=10),
                  response=rnorm(40))
women <- data.frame(grp=rep(letters[c(2:5, 7)], each=10),
                    response=rnorm(50))

## Determine all levels used, the number of levels, and appropriate
## xlim for the plot
grp.levs <- sort(unique(c(levels(men$grp), levels(women$grp))))
nlevs <- length(grp.levs)
xlim <- c(.5, nlevs+.5)

## Determine which of the levels are present in men and women; these
## are the x coordinates to draw the boxes (this will need tweaking if
## you are using ordered factors).
at.men <- match(levels(men$grp), grp.levs)
at.women <- match(levels(women$grp), grp.levs)

par(mfrow=c(2,1))
## boxplot() does not take an xlim argument, so you'll have to set up
## the plot yourself (including the axis, since the default is not
## appropriate for a boxplot).
plot(NA, type="n", xlim=xlim, ylim=range(men$response), xlab="",
     ylab="Response", xaxt="n")
axis(1, 1:nlevs, grp.levs)
boxplot(response ~ grp, men, at=at.men, add=TRUE)

plot(NA, type="n", xlim=xlim, ylim=range(women$response),
     xlab="Group", ylab="Response", xaxt="n")
axis(1, 1:nlevs, grp.levs)
boxplot(response ~ grp, women, at=at.women, add=TRUE)

Cheers,
Rich


On 4/20/05, Chris Evans <chris at psyctc.org> wrote:
> v 2.0.1 (sooooh old!) on Win2k
> 
> I think I know the answer to this but I can hope ...
> 
> I have data for continuous variables (measures of residents) by a
> categorical variable in range (1,22), the units in which they live.
> 
> I want to plot these data with a pair of boxplots one above another
> with same x-axis (1,22) using par(mfrow=c(2,1)) and then plotting
> first for the women then for the men.  My problem is that some units
> have only men, some have only women, and some have both.  I'd like
> both plots to have the same x axis and the notched, varwidth boxplots
> to locate themselves with some gaps so that the units are in the same
> place on the x axis on each plot.
> 
> I think that I can't do this with boxplot or bxp as both work out the
> x axis from the work that boxplot has done on the data.  Although
> there also seem to be useful extensions or alternative boxplots in
> other packages, I can't see one that does what I want and I think
> that rolling my own from bxp is really beyond my skills.
> 
> Am I right that it doesn't exist in the CRAN packages?  If not,
> apologies and point me where I should look?  If I am right (boo hoo!)
> I don't suppose anyone has written this or is feeling like
> demonstrating their personal genius with R coding?!!!  If they were,
> I don't think I'd be the only one to end up owing them a great deal
> of gratitude!
> 
> Thanks as ever to all who have made and continue to make R what it
> is: brilliant!
> 
> Chris
> 
> --
> Chris Evans <chris at psyctc.org>
> Consultant Psychiatrist in Psychotherapy, Rampton Hospital;
> Research Programmes Director, Nottinghamshire NHS Trust,
> Hon. SL Institute of Psychiatry
> *** My views are my own and not representative of those institutions
> ***
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
> 


-- 
Rich FitzJohn
rich.fitzjohn <at> gmail.com   |    http://homepages.paradise.net.nz/richa183
                      You are in a maze of twisty little functions, all alike