title: What is the best way to update last row of DataFrame?
body: <p>I want to update last row of DataFrame.<br>
  But, what is the best way to update it?  </p>
  
  <p>I just want to update like following data.<br>
  Any suggestion?</p>
  
  <pre><code>time A B C
  2019-01-01 1 2 3
  2019-01-02 4 5 6
  2019-01-03 7 8 9
  </code></pre>
  
  <p>↓</p>
  
  <pre><code>time A B C
  2019-01-01 1 2 3
  2019-01-02 4 5 6
  2019-01-03 10 11 12
  </code></pre>