title: Mapping values from one DataFrame to another
body: <p>I am trying to figure out some fast and clean way to map values from one <code>DataFrame</code> <code>A</code> to another. Let say I have <code>DataFrame</code> like this one:</p>
  
  <pre><code>    C1  C2  C3  C4  C5
  1   a   b   c   a
  2   d   a   e   b   a
  3   a   c
  4   b   e   e
  </code></pre>
  
  <p>And now I want to change those letter codes to actual values. My <code>DataFrame</code> <code>B</code>with explanations looks like that:</p>
  
  <pre><code>    Code    Value
  1   a       'House'
  2   b       'Bike'
  3   c       'Lamp'
  4   d       'Window'
  5   e       'Car'
  </code></pre>
  
  <p>So far my brute-force approach was to just go through every element in <code>A</code> and check with <code>isin()</code> the value in <code>B</code>. I know that I can also use <code>Series</code> (or simple dictionary) as an <code>B</code> instead of <code>DataFrame</code> and use for example <code>Code</code> column as a index. But still I would need to use multiple loops to map everything.</p>
  
  <p>Is there any other nice way to achieve my goal?</p>