[R] Boxplot Help: Re-ordering the x-axis

[Marc Schwartz (via MN)]

On Thu, 2006-08-17 at 11:46 -0700, Pamela Allen wrote:
> I am having a problem using boxlpot with my data.  I have my data arranged
> in a data table, and two of my columns are "mass" and "month".  I am trying
> to plot the mass of my study animals by month, thus I would like to have it
> in the order of January to December.  The problem is that R orders each
> month in alphabetical order, and gives each month an integer value
> corresponding to this (i.e. April is integer=1, August=2, September=12).  I
> have tried many different ways to solve this but nothing is working.  If
> anyone knows how to order the x-axis in boxplot, or alternatively, re-assign
> integer values to each month that would be very helpful.  Thank you in
> advance!  

Note the following in the Details section of ?boxplot:

"If multiple groups are supplied either as multiple arguments or via a
formula, parallel boxplots will be plotted, in the order of the
arguments or the order of the levels of the factor (see factor)."


If you are using a formula approach, then something like the following:

month <- factor(month, 
                levels = c("January", "February", 
                            ...,                 
                           "November", "December")

boxplot(mass ~ month)


See ?factor


For future reference, using:

  > RSiteSearch("boxplot order")

will search the r-help archive using the indicated key words, where you
will see that this has been covered previously.

HTH,

Marc Schwartz