title: Value error when calculating standard deviation on dataframe
body: <p>I need the standard deviation of column <code>distance</code> for each row in my dataframe.</p>
  <p>Dataframe <code>df_stats</code>:</p>
  <pre><code>                                a1/a2   distance  mean_distance
  date_time                                                      
  2021-10-29T21:00:00+00:00  105.007574  -2.530492       0.234318
  2021-10-29T22:00:00+00:00  104.459527  -5.232787       0.012537
  2021-10-29T23:00:00+00:00  104.648467   1.807101       0.093432
  2021-10-30T00:00:00+00:00  104.758201   1.048046       0.164502
  2021-10-30T01:00:00+00:00  104.820132   0.591004       0.246095
  2021-10-30T02:00:00+00:00  104.474062  -3.307024      -0.194917
  2021-10-30T03:00:00+00:00  104.284146  -1.819483      -0.231843
  2021-10-30T04:00:00+00:00  104.072383  -2.032697      -0.249918
  2021-10-30T05:00:00+00:00  103.690546  -3.675699      -0.484996
  2021-10-30T06:00:00+00:00  103.755979   0.630837      -0.823674
  2021-10-30T07:00:00+00:00  102.721667 -10.018720      -1.181811
  2021-10-30T08:00:00+00:00  102.998153   2.687995      -1.015365
  2021-10-30T09:00:00+00:00  103.236159   2.308109      -0.876012
  2021-10-30T10:00:00+00:00  103.471932   2.281216      -0.930593
  2021-10-30T11:00:00+00:00  103.376928  -0.918579      -1.142659
  2021-10-30T12:00:00+00:00  103.587805   2.037809      -1.110613
  2021-10-30T13:00:00+00:00  104.359756   7.424508      -0.468987
  2021-10-30T14:00:00+00:00  104.612493   2.418853      -0.383811
  2021-10-30T15:00:00+00:00  104.607392  -0.048755      -0.562828
  2021-10-30T16:00:00+00:00  104.846049   2.278849      -0.203495
  2021-10-30T17:00:00+00:00  104.997437   1.442872      -0.004827
  </code></pre>
  <p>Trying to do it this way:</p>
  <pre><code>df_stats['std'] = df_stats.distance.std(axis=1)
  </code></pre>
  <p>But I get this error:</p>
  <pre><code>No axis named 1 for object type &lt;class 'pandas.core.series.Series'&gt;
  </code></pre>
  <p>Why is it not working?</p>