title: title of subplots in stata marginsplot
body: <p>I have a question about setting the titles of subplots produced with the <code>marginsplot</code> command in stata. I very often need to adjust these, particularly when I plot three-way interactions. By default stata uses the value labels of the variable which is specified to provide the subdimensions in the <code>by</code> part of the <code>marginsplot</code> command. This works fine if the variable only has integer values, because as soon as one is working with values which has fractions labeling does not work anymore (e.g. an index from 0 to 1). I know that I could always multiply and get integer numbers but then I might be introducing other probelms, so I wanted to keep the original variable as it is and adjust the labels in the plot command. I have tried both with <code>byopt(title(""))</code> and with <code>title("")</code> but it did not work. </p>
  
  <p>Here is an example:</p>
  
  <pre><code>sysuse auto, clear
  
  lab drop origin
  
  reg price c.mpg##i.foreign##c.trunk
  
  margins, at(foreign=(0(1)1) mpg=(12 (2) 41) trunk=(10 14 17)) vsquish
  marginsplot, recastci(rline) by(foreign) byopt(title("") rows(1)) allsimplelabels ///
  ci1opts(lpattern("shortdash_dot") lwidth("medium") lcolor("gs6")) ///
  ci2opts(lpattern("shortdash_dot") lwidth("medium") lcolor("black")) ylabel(,gstyle(minor)) ///
  ci3opts(lpattern("shortdash_dot") lwidth("medium") lcolor("gs12")) ylabel(,gstyle(minor)) ///
  title("") legend(pos(6) col(3))
  </code></pre>
  
  <p>Note that if I do not drop the label in the beginning, the plot looks fine. That's what I would like to achieve without using value labels, only in the command used to get the plot. Any idea how to do that?</p>