title: Align x axis with grid.arrange
body: <p>I'm trying to plot two aligned graphics, but one of them has a label and of them doesn't.</p>
  
  <p>Example:</p>
  
  <pre><code>library(dplyr)
  library(ggplot2)
  
  df &lt;-
    seq(as.Date("2019-01-01"), as.Date("2019-01-31"), by = 1) %&gt;%
    as_tibble() %&gt;%
    rename(day = value) %&gt;%
    mutate(
      x = seq(1, 31, by = 1),
      y = x * 2 - 20
    )
  
  p1 &lt;-
    df %&gt;%
    gather(key, value, c(x, y)) %&gt;%
    ggplot(aes(x = day, y = value, color = key)) +
    geom_line(size = 1)
  
  p2 &lt;-
    df %&gt;%
    ggplot(aes(x = day, y = y / x)) +
    geom_line(size = 1)
  
  grid.arrange(
    p1, p2
  )
  </code></pre>
  
  <p>Result:</p>
  
  <p><a href="https://i.stack.imgur.com/arBUS.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/arBUS.png" alt="enter image description here"></a></p>
  
  <p>Is there a way to align the axis <strong>without using facet_wrap</strong>? (I want to add specific label formatters for each plot because they are in different units and facet_wrap doesn't allow me to do that as far as I know)</p>