title: Remove duplicates within a string, but for the entire dataframe
body: <p>I want to achieve something like in this post: <a href="https://stackoverflow.com/questions/47316783/python-dataframe-remove-duplicate-words-in-the-same-cell-within-a-column-in-pyt">Python Dataframe: Remove duplicate words in the same cell within a column in Python</a>, but for the entire dataframe in a efficient way. </p>
  
  <p>My data looks something like this: It is a pandas data frame with a lot of columns. It has comma separated strings where there are a lot of duplicates - and I wish to remove all duplicates within those individual strings.</p>
  
  <pre><code>+--------------------+---------+---------------------+
  |        Col1        |  Col2   |        Col3         |
  +--------------------+---------+---------------------+
  | Dog, Dog, Dog      | India   | Facebook, Instagram |
  | Dog, Squirrel, Cat | Norway  | Facebook, Facebook  |
  | Cat, Cat, Cat      | Germany | Twitter             |
  +--------------------+---------+---------------------+
  </code></pre>
  
  <p>Reproducable example:</p>
  
  <pre><code>df = pd.DataFrame({"col1": ["Dog, Dog, Dog", "Dog, Squirrel, Cat", "Cat, Cat, Cat"],
                       "col2": ["India", "Norway", "Germany"],
                       "col3": ["Facebook, Instagram", "Facebook, Facebook", "Twitter"]})
  </code></pre>
  
  <p>I would like it to transform it to this:</p>
  
  <pre><code>+--------------------+---------+---------------------+
  |        Col1        |  Col2   |        Col3         |
  +--------------------+---------+---------------------+
  | Dog                | India   | Facebook, Instagram |
  | Dog, Squirrel, Cat | Norway  | Facebook            |
  | Cat                | Germany | Twitter             |
  +--------------------+---------+---------------------+
  </code></pre>