title: add column data frame
body: <p>I would to add to the CellID column a number in the way to classify them.
  The dataframe is this:</p>
  <pre><code>umap
                             CellID  wnnUMAP_1  wnnUMAP_2
  0      KO_d0_r1:AAACAGCCACCTGCTCx  -8.127543   1.593849
  1      KO_d0_r2:AAACAGCCACGTAATTx  -7.246094  -4.566527
  2      HT_d0_r1:AAACAGCCATAATGAGx   7.617473   2.449949
  3      HT_d0_r2:AAACATGCACCTAATGx  -7.944949   6.633856
  </code></pre>
  <p>And my resoult would be this one</p>
  <pre><code> umap
                                 CellID    wnnUMAP_1   wnnUMAP_2
      0      KO_d0_r1:AAACAGCCACCTGCTCx-0  -8.127543   1.593849
      1      KO_d0_r2:AAACAGCCACGTAATTx-1  -7.246094  -4.566527
      2      HT_d0_r1:AAACAGCCATAATGAGx-2   7.617473   2.449949
      3      HT_d0_r2:AAACATGCACCTAATGx-3  -7.944949   6.633856
  </code></pre>
  <p>I would to add the <code>0 to KO_d0_r1, a -1 to KO_d0_r2, a -2 to HT_do_r1 and a -3 HT_d0_r2.</code>
  This is just an example, I have a lot of strings that have the prefix <code>KO_d0_r1</code>, ecc., so I would to distinguish them by the suffix.
  My attempt was:</p>
  <pre><code>umap = umap.rename(columns = {'Unnamed: 0':'CellID'})
  </code></pre>
  <p>But it doesn't work</p>