title: Drawing lines on scatter with Seaborn
body: <p>My objective is to draw a horizontal red line on y = 0 on a plot made using seaborn: <code>sns.lmplot</code>splitted by <code>col=</code> or <code>row=</code>.</p>
  
  <pre><code>import numpy as np, seaborn as sns, pandas as pd
  np.random.seed(5)
  
  myData = pd.DataFrame({'x' :  np.arange(1, 101), 'y': np.random.normal(0, 4, 100),\
  'z' : ['a','b']*50, 'w':np.random.poisson(0.15,100)})
  
  
  sns.lmplot("x", "y", col="z", row="w", data=myData, fit_reg=False)
  plt.plot(np.linspace(-20,120,1000), [0]*1000, 'r-')
  </code></pre>
  
  <p>We can see that only the last plot, of the array of plots, is marked by the red line:</p>
  
  <p><a href="https://i.stack.imgur.com/v1YnW.png" rel="noreferrer"><img src="https://i.stack.imgur.com/v1YnW.png" alt="enter image description here"></a></p>
  
  <p>Thanks for your help,</p>
  
  <p><strong>EDIT:</strong> reworded the question to account for the case where we generate an array of plots using <code>col=</code> and/or <code>row=</code> and we want the line to be traced on each plot.</p>