title: Extract data frame rows with certain conditions
body: <p>I have a data frame, two variables of <code>V1</code> and <code>V2</code>, with 9 rows of data. </p>
  
  <pre><code>Original Data Frame:
  
                   Var1       Var2 
      sigma1       11          1
      alpha1       12          5
      pi1          13          3
      sigma2       14          4
      alpha2       21          9
      pi2          34          6
      sigma3       55          12
      alpha3       18          9
      pi3          19          10
  </code></pre>
  
  <p>I want to separate all observations of alpha's, sigma's, and pi's. And make each of them to be a new data frame.</p>
  
  <pre><code>Ideal format afterwards:
  
      Data Frame 1:
  
          sigma1       11          1
          sigma2       14          4
          sigma3       55          12
  
      Data Frame 2:
  
          alpha1       12          5
          alpha2       21          9
          alpha3       18          9
  
      Data Frame 3:
  
          pi1          13          3
          pi2          34          6
          pi3          19          10
  </code></pre>
  
  <p>I want to separate all observations of alpha's, sigma's, and pi's. And make each of them to be a new data frame.</p>