title: Combine two dataframes according to the values in one of the columns
body: <pre><code>dataframe1
  data_a           data_b      data_c    data_d    data_e
  61               0.30792          Rest 2.34857    True
  183              0.93408          Rest 2.34550    True
  305              1.56019          Rest 2.34215    True
  427              2.18636          Rest 2.33955    True
  549              2.81252          Rest 2.33660    True
  
  dataframe2
  data_a           data_b      data_c    data_d    data_e
  122              0.62616     Discharge 2.32013   False
  244              1.25233     Discharge 2.31390   False
  366              1.87844     Discharge 2.31087   False
  488              2.50460     Discharge 2.30819   False
  610              3.13077     Discharge 2.30567   False
  </code></pre>
  <p>I would like the out put to be as follows:</p>
  <pre><code>dataframe3
  data_a           data_b      data_c    data_d    data_e
  61               0.30792          Rest 2.34857    True
  122              0.62616     Discharge 2.32013   False
  183              0.93408          Rest 2.34550    True
  244              1.25233     Discharge 2.31390   False
  305              1.56019          Rest 2.34215    True
  366              1.87844     Discharge 2.31087   False
  427              2.18636          Rest 2.33955    True
  488              2.50460     Discharge 2.30819   False
  549              2.81252          Rest 2.33660    True
  610              3.13077     Discharge 2.30567   False
  </code></pre>
  <p>As you can see, the new dataframe should be sorted by according to the sequential order of the values in the data_a column.</p>