title: Normalize multiindex dataframe in pandas
body: <p>I am trying to normalize multiindex dataframe: subtract it's mean and divide by its standard deviation. That's how you do it with a normal (not multiindex) dataframe:</p>
  
  <pre><code>df4 = (df4-df4.mean(1)) / df.std(1)
  </code></pre>
  
  <p>However, with the multiindex dataframe it does not work: I am getting this absurdish error:</p>
  
  <pre><code>ValueError: cannot join with no level specified and no overlapping names
  </code></pre>
  
  <p>So I wonder if there is work-around, simpler than flattening and de-flattening the index?</p>