title: Python - Remove rows if criteria does not exist
body: <p>Provided the three columns, I am looking to remove all IDs that do not have an indicator of Y that is equal to or less than 28 DateDiff. The Datediff column is the number of days from an initial incident.</p>
  <pre><code>df = pd.DataFrame({'ID':[111, 111, 111, 112, 112, 112, 113, 114, 114, 115,
                                                                   115],
                     'Indicator':['N', 'Y', 'N', 'N', 'N', 'N', 'N', 'Y',
                                                           'N', 'Y', 'N'],
                     'Dateddiff': [0, 10, 32, 0, 19, 37, 29, 0, 28, 30, 34]})
  </code></pre>
  <p>Input</p>
  <pre><code>ID   Indicator Datediff
  111  N         0
  111  Y         10
  111  N         32
  112  N         0
  112  N         19
  112  N         37
  113  N         29  
  114  Y         0
  114  N         28
  115  Y         30
  115  N         34
  </code></pre>
  <p>Output</p>
  <pre><code>ID   Indicator Datediff
  111  N         0
  111  Y         10
  111  N         32
  114  Y         0
  114  N         28
  </code></pre>