title: Stacked dataframe into a two column time-series
body: <p>I have a stacked dataframe that looks like this:</p>
  <pre><code>YEAR    
  1973  1     26.18
        2     26.18
        3     25.53
  ...
  1974  1     24.53
        2     24.89
        3     24.17
  ...
  1975  1     24.21
        2     24.98
        3     25.47
  </code></pre>
  <p>The numbers in the index represent the month that the data was taken and I'm looking to get a dataframe that looks something like this:</p>
  <pre><code>Date   
  1-1973     26.18
  2-1973     26.18
  3-1973     25.53
  ...
  1-1974     24.53
  2-1974     24.89
  3-1974     24.17
  ...
  1-1975     24.21
  2-1975     24.98
  3-1975     25.47
  </code></pre>
  <p>Does anyone know of a way I could pull this off?</p>
  <p>I tried unstacking the dataframe which gave me something like this:</p>
  <pre><code>1   2   3   4   5   6   7   8   9   10  11  12
  YEAR                                                
  1973    26.18   26.18   25.53   24.52   22.63   22.35   21.10   22.45   23.34   23.47   24.12   24.75
  1974    24.53   24.89   24.17   23.82   22.29   20.19   19.38   21.41   23.97   24.67   23.37   23.57
  1975    24.21   24.98   25.47   22.99   24.22   20.38   19.45   20.98   22.73   25.10   24.04   23.97
  1976    25.39   24.87   25.44   24.39   22.71   21.65   21.05   22.26   23.73   23.31   23.59   24.42
  </code></pre>
  <p>But this is not quite what I'm looking for.</p>
  <p>Thanks for the help!</p>