title: Adjusting y axis limits in ggplot2 with facet and "free" scales
body: <p>Here is the plot I can make:</p>
  <pre class="lang-r prettyprint-override"><code>data &lt;- data.frame(Patient = rep(seq(1, 5, 1), 2),
                     Treatment = c(rep(&quot;Pre&quot;, 5), rep(&quot;Post&quot;, 5)),
                     Gene.1 = c(rnorm(5, 10, 5), rnorm(5, 50, 5)),
                     Gene.2 = c(rnorm(5,10,5), rnorm(5, 10, 5)))
  
  data %&gt;%
    gather(Gene, Levels, -Patient, -Treatment) %&gt;%
    mutate(Treatment = factor(Treatment, levels = c(&quot;Pre&quot;, &quot;Post&quot;))) %&gt;%
    mutate(Patient = as.factor(Patient)) %&gt;%
    ggplot(aes(x = Treatment, y = Levels, color = Patient, group = Patient)) +
    geom_point() +
    geom_line() +
    facet_wrap(. ~ Gene, scales = &quot;free&quot;) +
    theme_bw() +
    theme(panel.grid = element_blank())
  </code></pre>
  <p><img src="https://i.stack.imgur.com/wa3LZ.jpg" alt="Example plot" /></p>
  <p>The &quot;free&quot; scales function is wonderful, however, I would like to make these two specifications/adjustments:</p>
  <ol>
  <li><p>Y axis begins at 0</p>
  </li>
  <li><p>Increase the upper y limit by ~10% so that I have some space to add some annotations later on (p-values, etc.) in photoshop.</p>
  </li>
  </ol>
  <p>An alternative strategy might be to make the individual plots and assemble them together, though, this gets a little tedious with many facet elements.</p>