title: Combining FacetGrid and dual Y-axis in Pandas
body: <p>I am trying to plot two different variables (linked by a relation of causality), <code>delai_jour</code> and <code>date_sondage</code> on a single FacetGrid. I can do it with this code:</p>
  
  <pre><code>g = sns.FacetGrid(df_verif_sum, col="prefecture", col_wrap=2, aspect=2, sharex=True,)
  g = g.map(plt.plot, "date_sondage", "delai_jour", color="m", linewidth=2)
  g = g.map(plt.bar, "date_sondage", "impossible")
  </code></pre>
  
  <p>which gives me this:</p>
  
  <p><a href="https://i.stack.imgur.com/KOV1b.png" rel="nofollow noreferrer">FacetGrid</a></p>
  
  <p>(There are 33 of them in total).</p>
  
  <p>I'm interested in comparing the patterns across the various <code>prefecture</code>, but due to the difference in magnitude I cannot see the changes in the line chart. </p>
  
  <p>For this specific work, the best way to do it is to create a secondary y axis, but I can't seem to make anything work: it doesn't look like it's possible with FacetGrid, and I didn't understand the code not was able to replicate the examples i've seen with pure matplotlib.</p>
  
  <p>How should I go about it?</p>