title: find max value of a list with numpy nan
body: <pre><code>import numpy as np
  
  print max([np.nan, 1, 2, 3, 4])
  print max([1, 2, 3, 4, np.nan])
  print max([1, 2, 3, np.nan, 4])
  </code></pre>
  
  <p>the first will print nan as list's max value</p>
  
  <p>the second will print 4 as list's max value</p>
  
  <p>the third will print 4 as list's max value</p>
  
  <p>Is there a solution for this problem? Make all math function just ignore nan?</p>