title: ggplot geom_errorbar width when faceting (and scale="free")
body: <p>I'm trying to create a faceted plot using ggplot and geom_errorbar.  However, each different facet may have have vastly different x ranges, and so the width of the error bar isn't looking "good".  Here's a MWE:</p>
  
  <pre><code>library(ggplot2)
  test &lt;- data.frame( group=rep(c(1,2,3),each=10), ymin=rnorm(30), ymax=rnorm(30))
  test$x &lt;- rnorm(30) * (1+(test$group==1)*20)
  ggplot( test, aes(x=x, ymin=ymin, ymax=ymax) ) +
    geom_errorbar(width=5) + facet_wrap( ~ group, scale="free_x" )
  ggplot( test, aes(x=x, ymin=ymin, ymax=ymax) ) +
    geom_errorbar(width=.2) + facet_wrap( ~ group, scale="free_x" )
  </code></pre>
  
  <p>In the first plot, the error bars for group 1 look great, but 2 and 3 are far too wide.  In the second plot, the error bars are way too small for group 1.  Is there an easy way to fix this?  I'm thinking I might just have to use width=0, but I'd like to avoid that.</p>
  
  <p><img src="https://i.stack.imgur.com/IAexu.png" alt="First Plot"></p>
  
  <p><img src="https://i.stack.imgur.com/09X5G.png" alt="Second Plot"></p>