title: Filtering a dataframe in row names from a column values
body: <p>Basically I have dataframe with two columns (<code>target_id</code> and <code>fpkm</code>). I want to keep only those row names in first column that are not duplicated.<br>
  For example in the below dataframe you can see there are two row names with the same name (almost) <code>comp267138_c0_seq1</code> <code>comp267138_c0_seq2</code> and from both and I want to keep only one <code>comp267138_c0_seq2</code> based of high value in column 2.</p>
  
  <pre><code>       target_id        fpkm
  comp247393_c0_seq1    3.197885
  comp257058_c0_seq4    1.624577
  comp242590_c0_seq1    1.750319
  comp77911_c0_seq1     1.293059
  comp241426_c0_seq1    1.626589
  comp288413_c0_seq1   14.828853
  comp294436_c0_seq1   11.555596
  comp63603_c0_seq1     1.982386
  comp267138_c0_seq1    8.594494
  comp267138_c0_seq2   11.134958
  comp321623_c0_seq1    6.934149
  </code></pre>