title: ValueError: Contour levels must be increasing - how to plot 3 feature data
body: <pre><code>import numpy as np
  from matplotlib import pyplot as plt
  
  data = np.random.normal(0,1,[100,3])
  
  x = data[:,0]
  y = data[:,1]
  
  z = data[:,2]
  
  plt.contour([x,y],z)
  </code></pre>
  
  <p>When I run this code with dummy data I get:</p>
  
  <pre><code>ValueError: Contour levels must be increasing
  </code></pre>
  
  <p>Do you have any idea what would this mean and how I could fix it?</p>