title: How to get only distinct values from a list?
body: <p>I am trying to iterate through a column in a text file, where each entry has only three choices  <code>A, B, and C</code>. </p>
  
  <p>I want to identify the number of different types of choices <code>(another text file has A, B, C, and D)</code>, but if I iterate through each element in the column with a <code>100 entries</code> and add it to a list, I'll have multiple repetitions of each type. For example, if I do this, the list might read <code>[A,A,A,B,C,C,D,D,D,B,B...]</code>, but I want to remove the extraneous entries and just have my list show the distinguishable types <code>[A,B,C,D]</code>, regardless of how many entries there were. </p>
  
  <p>Any ideas how I might reduce a list with many common elements to a list with only the different distinguishable elements displayed? Thanks!</p>
  
  <p>Desired Output:</p>
  
  <p><code>[A, B, C, D]</code></p>