title: Comparing many timestamps with pandas
body: <p>I have two dataframes with different sizes containing timestamps. I need to find nearest timestamps. In df A I need to find all first timestamps after any of timestamps of df B. The dataframes have each around 100,000 rows so iteration is not a way and even <code>df.apply()</code> took around 6 mins.</p>
  
  <p>e.g.:</p>
  
  <pre><code>A:
  11
  12
  15
  16
  18
  20
  25
  30
  50
  
  B:
  14
  19
  22
  27
  
  result:
  15
  20
  25
  30
  </code></pre>