title: LabelEncoder: How to keep a dictionary that shows original and converted variable
body: <p>When using <code>LabelEncoder</code> to encode categorical variables into numerics, </p>
  
  <p>how does one keep a dictionary in which the transformation is tracked?</p>
  
  <p>i.e. a dictionary in which I can see which values became what:</p>
  
  <pre><code>{'A':1,'B':2,'C':3}
  </code></pre>