title: Normalize pandas dataframe with all columns together
body: <p>I want to normalize a pandas dataframe with all columns together</p>
  
  <pre><code>In [8]: df
  Out[8]:
     x  y
  0  1  2
  1  2  3
  2  3  4
  </code></pre>
  
  <p>I do   </p>
  
  <pre><code>df_nor = (df-df.min())/(df.max()-df.min())
  </code></pre>
  
  <p>OUT:</p>
  
  <pre><code>In [10]: df_nor
  Out[10]:
       x    y
  0  0.0  0.0
  1  0.5  0.5
  2  1.0  1.0
  </code></pre>
  
  <p>How can I get column x and y be normalized together like</p>
  
  <pre><code>In [10]: df_nor
  Out[10]:
       x    y
  0  0.000  0.333
  1  0.333  0.666
  2  0.666  1.000
  </code></pre>
  
  <p>Thanks!</p>