title: get specified indexes of pandas dataframe where column has condition
body: <p>I have a pandas dataframe:</p>
  <pre><code>id    value
  14     122
  15     120
  16     190
  17     490
  18     328
  19     309
  20     323
  </code></pre>
  <p>I have a list of id's <code>L = [14,17,20]</code> and want to do two things:</p>
  <blockquote>
  <p>Get the list of indexes of those rows where for the id's is not in the list L</p>
  <p>i.e.( index of rows 15,16,18,19)</p>
  </blockquote>
  <p>and,</p>
  <blockquote>
  <p>Delete the rows for the id's is not in the list L.</p>
  </blockquote>
  <p>My expected output:</p>
  <pre><code>id    value
  14     122
  17     490
  20     323
  </code></pre>