title: Split data frame in two disjoint sub frames based on row index
body: <p>How can I split a dataframe</p>
  
  <pre><code>import pandas as pd
  import numpy as np
  np.random.seed(0)
  df = pd.DataFrame({'first':np.random.rand(4),'second':np.random.rand(4)},index=['foo','bar','baz','bat'])
  print(df)
          first    second
  foo  0.548814  0.423655
  bar  0.715189  0.645894
  baz  0.602763  0.437587
  bat  0.544883  0.891773
  </code></pre>
  
  <p>into the two following disjoint data frames </p>
  
  <pre><code>        first    second
  foo  0.548814  0.423655
  bar  0.715189  0.645894
  
       first    second
  baz  0.602763  0.437587
  bat  0.544883  0.891773
  </code></pre>
  
  <p>by using the indices for the first data frame?</p>
  
  <p>I am specifically looking for a method like</p>
  
  <pre><code>subDf1,subDf2 = pd.split(df,['foo','bar'])
  </code></pre>
  
  <p>where </p>
  
  <pre><code>print(subDf1)
     first    second
  foo  0.548814  0.423655
  bar  0.715189  0.645894
  </code></pre>
  
  <p>and</p>
  
  <pre><code>print(subDf2 )
    first    second
  baz  0.602763  0.437587
  bat  0.544883  0.891773
  </code></pre>