title: Insert line in heatmap after every 7th column
body: <p>can someone help me how to add a veritcal line after every 7th column in my plot here?</p>
  <p><a href="https://i.stack.imgur.com/PjAsK.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/PjAsK.png" alt="enter image description here" /></a></p>
  <p>So I want to have after the new M1 starts a thick vertical line here.. Has someone an idea?
  My code is:</p>
  <pre><code>piv = pd.pivot_table(df2, values=&quot;Corr&quot;,index=[&quot;GABA Receptor&quot;], columns=[&quot;Experiment&quot;], fill_value=0)
  ax= sns.heatmap(piv, xticklabels=True, vmin=0, vmax=0.5)
  # fix for mpl bug that cuts off top/bottom of seaborn viz
  b, t = plt.ylim() # discover the values for bottom and top
  b += 0.5 # Add 0.5 to the bottom
  t -= 0.5 # Subtract 0.5 from the top
  plt.ylim(b, t) # update the ylim(bottom, top) values
  plt.show() # ta-da!
  plt.title('Chronification Group')
  plt.xticks(fontsize=10, rotation=90)
  # fix for mpl bug that cuts off top/bottom of seaborn viz
  b, t = plt.ylim() # discover the values for bottom and top
  b += 0.5 # Add 0.5 to the bottom
  t -= 0.5 # Subtract 0.5 from the top
  plt.ylim(b, t)
  </code></pre>