title: how to plot geom_col() to get y axis to center around 1 and not 0
body: <p>I am plotting a some data using <code>ggplot2</code>'s <code>geom_bar</code>. The data represents a ratio that should center around <code>1</code> and not <code>0</code>.  This would allow me to highlight which categories go below or above this central ratio number. I've tried playing with <code>set_y_continuous()</code> and <code>ylim()</code>, neither of which allow me to sent a central axis value. </p>
  
  <p>Basically: how to I make <code>Y</code> center around <code>1</code> and not <code>0</code>.</p>
  
  <p>sorry if i am asking a question that's been answered... maybe I just don't know the right key words?</p>
  
  <pre><code>ggplot(data = plotdata) +
    geom_col(aes(x = stressclass, y= meanexpress, color = stressclass, fill = stressclass)) +
    labs(x = "Stress Response Category", y = "Average Response Normalized to Control") +
    facet_grid(exposure_cond ~ .)
  </code></pre>
  
  <p>As of now my plots look like this: </p>
  
  <p><a href="https://i.stack.imgur.com/fEMeg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fEMeg.png" alt="enter image description here"></a></p>