title: Multiple scatter plot on same axis
body: <p>I have 3 scatter plots, was wondering how I can combine these 3 into 1 big scatter plot.</p>
  
  <p>I can't seem to find a solution to this specific problem using only Matplotlib.</p>
  
  <pre><code>x1 = np.random.randint(40, 100, 50)
  y1 = np.random.randint(40, 100, 50)
  
  x2 = np.random.randint(0, 60, 50)
  y2 = np.random.randint(0, 60, 50)
  
  x3 = np.random.randint(40, 100, 50)
  y3 = np.random.randint(0, 60, 50)
  
  fig, (plot1, plot2, plot3, plot4) = plt.subplots(1, 4)
  
  plot1.scatter(x1,y1, color='green', s = 10)
  plot1.set(xlim=(0, 100), ylim=(0, 100))
  
  plot2.scatter(x2,y2, color='red', s = 10)
  plot2.set(xlim=(0, 100), ylim=(0, 100))
  
  plot3.scatter(x3,y3, color='blue', s = 10)
  plot3.set(xlim=(0, 100), ylim=(0, 100))
  
  plot4.scatter(plot1, plot2, plot3)
  </code></pre>
  
  <p>so I want plot4 to be a combination of plot1, plot2 and plot3.</p>