boxplot question

I'm graphing a series of boxplots of grouped data inside a function that
passes the data.frame, the names vector, and a title vector.

Because both the data subset changes with each successive pass through the
function, occasionally the names vector turns up with only one group to
plot.  This is an expected result.  However, when the names argument in
boxplot has only a single name, it doesn't put in on the
boxplot.  (Actually, this is true whether the names argument is present or
not.  If the call to boxplot is in formula form (e.g. variable ~ group),
the plot doesn't name the group if there is only one group.)

Yes. In order to get around this you need to modify the bxp() function
that does the actual plotting.


My recommended change is to add a show.names argument:

  function (z, notch = FALSE, width = NULL, varwidth = FALSE, notch.frac =
  0.5,  boxwex = 0.8, border = par("fg"), col = NULL, log = "", pars =
  NULL, frame.plot = axes, horizontal = FALSE, add = FALSE, at = NULL,
  show.names=NULL, ...)

and then near the end of the function replace the if(axes) conditional
with

    if (axes) {
        ax.pars <- pars[names(pars) %in% c("xaxt", "yaxt", "las")]
	if(is.null(show.names)) show.names<-(n>1)
        if (show.names)
            do.call("axis", c(list(side = 1 + horizontal, at = at,
                labels = z$names), ax.pars))
        do.call("axis", c(list(side = 2 - horizontal), ax.pars))
    }


Now the standard behaviour is the same but you can override it with

  temp<-boxplot(y~g,plot=FALSE)
  bxp(temp,show.names=TRUE)

or if you have multiple groups but don't want names for some strange
reason
  bxp(temp,show.names=FALSE)


	-thomas

Thomas Lumley			Asst. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle

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