title: Filtering a dataframe showing only duplicates
body: <p>I need some help to filter a dataframe.</p>
  
  <p>The df has several columns and I want to split it into two dataframes:</p>
  
  <p>1- One including only the rows in which the first column is a duplicate (including all of the replicas).</p>
  
  <p>2- The rest of the rows, which are not duplicates.</p>
  
  <p>Here is an example:
  This would be the original.</p>
  
  <pre><code>          V1  V2 
      [1,] "A" "1"
      [2,] "B" "1"
      [3,] "A" "1"
      [4,] "C" "2"
      [5,] "D" "3"
      [6,] "D" "4"
  </code></pre>
  
  <p>I want to turn into this:</p>
  
  <pre><code>         V1  V2 
     [1,] "A" "1"
     [2,] "A" "1"
     [3,] "D" "3"
     [4,] "D" "4"
  </code></pre>
  
  <p>And this:</p>
  
  <pre><code>        V1  V2 
    [1,] "B" "1"
    [2,] "C" "2"
  </code></pre>
  
  <p>Is there a way to do that? I have tried exporting to Excel, but the dataset was too large to make that viable.</p>
  
  <p>Thank you</p>