title: Multiply two Series with MultiIndex in pandas
body: <p>I am trying to multiply two <code>Series</code>, both with <code>MultiIndex</code>:</p>
  
  <pre><code>import pandas as pd
  tuples = [(0, 100, 1000),(0, 100, 1001),(0, 100, 1002), (1, 101, 1001)]
  index_3levels=pd.MultiIndex.from_tuples(tuples,names=["l1","l2","l3"])
  tuples = [(0, 100), (1, 101)]
  index_2levels=pd.MultiIndex.from_tuples(tuples,names=["l1","l2"])
  data_3levels = pd.Series(1, index=index_3levels)
  data_2levels = pd.Series([2,3], index=index_2levels)
  print data_3levels  
  l1  l2   l3  
  0   100  1000    1
           1001    1
           1002    1
  1   101  1001    1
  dtype: int64
  print data_2levels
  l1  l2 
  0   100    2
  1   101    3
  dtype: int64
  </code></pre>
  
  <p>The problem is that I cannot reindex the <code>Series</code> from 2 to 3 levels:</p>
  
  <pre><code>data_2levels.reindex(data_3levels.index, level=["l1","l2"])
  Exception: Join on level between two MultiIndex objects is ambiguous
  </code></pre>
  
  <p>I found this workaround:</p>
  
  <pre><code>for l1 in [0,1]:
      data_3levels[l1] *= data_2levels[l1].reindex(data_3levels[l1].index, level="l2")
  print data_3levels
  l1  l2   l3  
  0   100  1000    2
           1001    2
           1002    2
  1   101  1001    3
  dtype: int64
  </code></pre>
  
  <p>But I think there should be a method to perform this operation in just 1 step.</p>