title: Pandas - Get dummies for only certain values
body: <p>I have a <code>Pandas</code> series of 10000 rows which is populated with a single alphabet, starting from A to Z. 
  However, I want to create dummy data frames for only A, B, and C, using Pandas <code>get_dummies</code>.
  How do I go around doing that?</p>
  
  <p>I don't want to get dummies for all the row values in the column and then select the specific columns, as the column contains other redundant data which eventually causes a Memory Error.</p>