title: How to remove rows in a dataframe considering there are duplicates in one column of dataframe
body: <p>Hi dear I have a little problem with a dataframe that has duplicates in a column. I would like to remove the rows where a column presents duplicates. For example my dataframe is like this:</p>
  
  <pre><code>Value   City    Card.Type   ID
  100   Michigan    Silver    001
  120   Angeles     Gold      002
  NA    Kansas      Gold      002
  500   Michigan    Silver    001
  800   Texas       Basic     005
  </code></pre>
  
  <p>You can see that in <code>ID</code> column there are two duplicates one for <code>001</code> and one for <code>002</code>. I was using <code>unique</code> function but I don't get to erase that duplicates. I would like to get someone like this:</p>
  
  <pre><code> Value   City    Card.Type   ID
   100   Michigan    Silver    001
   120   Angeles     Gold      002
   800   Texas       Basic     005
  </code></pre>
  
  <p>Thanks for your help.</p>