title: How to convert micro to milliseconds in one column and aggregate mode of another column in pandas
body: <p>I have a df with 2 columns. One is the timestamp in microseconds and the other is a a value. It looks like this:</p>
  <pre><code>         time  score
          83620      4
          83621      4
          83622      4
          83623      4
          83624      4
          83625      4
          83626      4
          83627      4
          83628      4
          83629      4
          83630      4
          83631      4
          83632      4
          83633      5
          83634      5
          83635      5
          83636      5
          83637      5
          83638      5
          83639      6
          83640      1
          83641      1
          83642      4
  </code></pre>
  <p>I want to concert df.time to milliseconds and aggregate df.score by the mode. It should look like this:</p>
  <pre><code>         time  score
          8362      4
          8363      5
          8364      1
         
  </code></pre>