title: Filter dataframe rows which contribute to X% of values in one column
body: <p>I have a dataframe:</p>
  <pre><code>df
  Col1   Col2   Col3
  A      B      5
  C      D      4
  E      F      1
  </code></pre>
  <p>I want to see only those rows which contribute to 90% of Col3. In this case the expected output will be :</p>
  <pre><code>Col1   Col2   Col3
  A      B      5
  C      D      4
  </code></pre>
  <p>I tried the below but is doesnt work as expected:</p>
  <pre><code>df['col3'].value_counts(normalize=True) * 100
  </code></pre>
  <p>Is there any solution for the same?</p>