title: Split value in pandas dataframe
body: <p>I have a panda dataframe with the following columns:</p>
  <pre><code>             Stock     ROC5   ROC20  ROC63    ROCmean
          0    IBGL.SW  -0.59   3.55   6.57     3.18
          0    EHYA.SW   0.98   4.00   6.98     3.99
          0    HIGH.SW   0.94   4.22   7.18     4.11
          0    IHYG.SW   0.56   2.46   6.16     3.06
          0    HYGU.SW   1.12   4.56   7.82     4.50
          0    IBCI.SW   0.64   3.57   6.04     3.42
          0    IAEX.SW   8.34  18.49  14.95    13.93
          0    AGED.SW   9.45  24.74  28.13    20.77
          0    ISAG.SW   7.97  21.61  34.34    21.31
          0    IAPD.SW   0.51   6.62  19.54     8.89
          0    IASP.SW   1.08   2.54  12.18     5.27
          0    RBOT.SW  10.35  30.53  39.15    26.68
          0    RBOD.SW  11.33  30.50  39.69    27.17
          0    BRIC.SW   7.24  11.08  75.60    31.31
          0    CNYB.SW   1.14   4.78   8.36     4.76
          0     FXC.SW   5.68  13.84  19.29    12.94
          0   DJSXE.SW   3.11   9.24   6.44     6.26
          0  CSSX5E.SW  -0.53   5.29  11.85     5.54
  </code></pre>
  <p>How can I write in the dataframe a new columns &quot;Symbol&quot; with the stock without &quot;.SW&quot;.
  Example first row result should be IBGL (modified value IBGL.SW).
  Example last row result should be CSSX5E (splited value SSX5E.SW).</p>
  <p>Is there a way to sort the values in the columns ROCmean ascending (sort last columns ascending)?</p>
  <p>If I send the following command:</p>
  <pre><code>new_df['Symbol'] = new_df.loc[:, ('Stock')].str.split('.').str[0]
  </code></pre>
  <p>Than I receive an error message:
  :3: SettingWithCopyWarning:
  A value is trying to be set on a copy of a slice from a DataFrame.
  Try using .loc[row_indexer,col_indexer] = value instead</p>
  <p>See the caveats in the documentation: <a href="https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#returning-a-view-versus-a-copy" rel="nofollow noreferrer">https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#returning-a-view-versus-a-copy</a></p>
  <pre><code> new_df['Symbol'] = new_df.loc[:, ('Stock')].str.split('.').str[0]
  </code></pre>
  <p>How can I solve this problem?</p>
  <p>Thanks a lot for your support.</p>