title: Replace values in dataframe based on rank
body: <p>I have the 2 following dataframes:</p>
  <p>Rank:</p>
  <pre><code>    A   B   C   D
  0   85  88  44  80
  1   22  34  80  92
  2   80  80   2  31
  </code></pre>
  <p>and Value:</p>
  <pre><code>          a         b         c         d
  0  0.671399  0.101208 -0.181532  0.241273
  1  0.446172 -0.243316  0.051767  1.577318
  2  0.614758  0.075793 -0.451460 -0.012493
  </code></pre>
  <p>In table &quot;Value&quot; I would like to replace all values for which rank is &gt; 80 with the value that has rank = 80 (by column)</p>
  <p>So far I have an iterative process that takes way too long and there surely is a pythonic way to do it with a mapping but I can't figure out the syntax.
  Thanks for the help</p>