title: why numpy max function(np.max) return wrong output?
body: <p>I have <code>pandas DataFrame</code> and I turn it to <code>numpy ndarray</code>.I use <code>max</code> function for one column in my DataFrame like this:</p>
  <pre><code>print('column: ',df[:,3])
  print('max: ',np.max(df[:,3]))
  </code></pre>
  <p>And the output was:</p>
  <pre><code>column: [0.6559999999999999 0.48200000000000004 0.9990000000000001 ..., 1.64 nan 0.07]
  max: 0.07
  </code></pre>
  <p>But as you can see for example first value is greater than  0.07!!
  What is the problem?</p>