title: Split a pandas dataframe into two dataframes efficiently based on some condition
body: <p>So, I want to split a given dataframe into two dataframes based on an if condition for a particular column.
  I am currently achieving this by iterating over the whole dataframe two times. Please suggest some ways to improve this.</p>
  
  <pre><code> player   score
   dan       10
   dmitri    45
   darren    15
   xae12     40
  </code></pre>
  
  <p>Like in the above dataframe, I want to split the df into two such that one df contains rows with the players scoring less than 15 and the other df contains the remaining rows. I want to this with one iteration only. (Also, if the answer can be generic for n dfs, it will help me a lot) 
  Thanks in advance.</p>