title: facet_wrap(scales="free_y") not producing desired result
body: <p>I am trying to create a plot using ggplot2 with 9 subplots. My goal is to allow the vertical axis to be scaled at the individual level for each of the 9 subplots. To that end, I am trying the syntax facet_wrap(scales = "free_y"). However, it does not appear to be working for me, and instead, the vertical axis seems to be identical across all 9 subplots. Below is a MWE:</p>
  
  <pre><code>x &lt;- rep(c(rep("F",4),rep("M",4)),9)
  y &lt;- abs(c(rnorm(36,0,20),rnorm(36,0,5)))
  z &lt;- rep(1:9,each=8)
  meanG1 &lt;- c()
  meanG2 &lt;- c()
  for (i in c(1,9,17,25,33,41,49,57,65)){
    meanG1 &lt;- c(meanG1, rep(mean(y[i:(i+3)]),8))
    meanG2 &lt;- c(meanG2, rep(mean(y[5:(i+3)]),8))
  }
  dat &lt;- data.frame(x=x,y=y,z=z,meanG1=meanG1,meanG2=meanG2)
  
  ggplot(dat, aes(x, y)) + 
    geom_point(aes(colour = factor(x)), shape = 20, size=5, alpha = 0.5) + 
    scale_shape(solid = FALSE) + 
    ggtitle(paste("My Plot")) + 
    ylab("Count") + 
    scale_y_continuous(limits=c(0, max(dat$y))) + 
    theme(axis.title.x = element_blank(), 
          legend.position="bottom", 
          axis.text=element_text(size=12), 
          axis.title=element_text(size=12), 
          legend.title=element_text(size=12), 
          legend.text=element_text(size=12), 
          plot.title=element_text(hjust=0.5)) + 
    labs(colour = "Group", size=12) + 
    geom_segment(aes(x = 1, y = meanG1, xend = 2, yend = meanG2), colour="gray25", size = 0.1) + 
    facet_wrap(~ z, ncol = 3, scales = "free_y")
  </code></pre>
  
  <p>If anyone has advice on what might be causing this and/or how to fix this, I would be all ears! Thank you.</p>