title: pandas groupby streak of numbers
body: <p>I have a dataframe like this:</p>
  
  <pre><code>df = pd.DataFrame({'dir':[0,0,0,1,1,0,1], 'price': [100, 102, 110, 120, 125, 200, 210]})
  
     dir  price
  0    0    100
  1    0    102
  2    0    110
  3    1    120
  4    1    125
  5    0    200
  6    1    210
  </code></pre>
  
  <p>and I want to groupby 0s and the 1s after it. My desired outcome looks like this:</p>
  
  <pre><code>   dir  price
  0    0    100
  1    0    102
  2    0    110
  3    1    120
  4    1    125
  
     dir  price
  5    0    200
  6    1    210
  </code></pre>