title: sorting pandas dataframe based on row frequency
body: <p>I have a pandas dataframe df:</p>
  
  <pre><code>Name Score
  AAAA    4
  AAAA    7
  AAAA   12
  AAAA   13
  BBBB    1
  BBBB    1
  CCCC    1
  CCCC    2
  CCCC   27
  </code></pre>
  
  <p>I want a new dataframe that has values from the df only if each "Name" occurs atleast 3 time. i.e. the desired output is</p>
  
  <pre><code>Name Score
  AAAA    4
  AAAA    7
  AAAA   12
  AAAA   13
  CCCC    1
  CCCC    2
  CCCC   27
  </code></pre>
  
  <p>I know df.groupby['Name'] gives the frequency of each name.
   Any suggestions how I can use this info in getting the desired output. Thanks</p>