R help - Aug 2006 - Boxplot Help: Re-ordering the x-axis

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!  

Pamela Allen, MSc Candidate
University of British Columbia
Marine Mammal Research Unit, Fisheries Centre
Vancouver, B.C.  V6T 1Z4
 
allen at zoology.ubc.ca

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

month.name
class(month.name)
character"
tmp <- data.frame(m=rep(month.name, 2), y=rnorm(24))
bwplot(y ~ m, data=tmp)

tmp <- data.frame(m=ordered(rep(month.name, 2), levels=month.name),
y=rnorm(24))
bwplot(y ~ m, data=tmp)