title: Drawing horizontal mean/average line across a scatterplot
body: <p>im trying to draw a straight horizontal line across all the mean of data points of the blue and red color.</p>
  <p>Right now, it looks like this
  <a href="https://i.stack.imgur.com/2CNjX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2CNjX.png" alt="enter image description here" /></a></p>
  <p>and this is my code for the above picture</p>
  <pre><code>fig=plt.figure(figsize=(20,10), dpi=100)
  ax=fig.add_axes([0,0,1,1])
  ax.scatter(x='Speed', y='Port ME Homemade Mass Flow Rate (kg/s)', data=df1before, color='r', marker='1')
  ax.scatter(x='Speed', y='Port ME Homemade Mass Flow Rate (kg/s)', data=df1after, color='b', marker='x')
  ax.set_xlabel('Speed(Knot)')
  ax.set_ylabel('Port ME Homemade Mass Flow Rate (kg/s)')
  #plt.plot(x=df3[len('Speed')], y=df3['Port ME Homemade Mass Flow Rate (kg/s)'].mean())
  plt.show()
  </code></pre>
  <p>The comment is what I have tried.. The desired output would be:
  <a href="https://i.stack.imgur.com/FHycF.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/FHycF.jpg" alt="enter image description here" /></a></p>
  <p>It would also be great if each line could show the value of position Y that it's at.</p>
  <p>Thanks!</p>