title: moving a row of a pandas dataframe but index unchanged
body: <pre class="lang-py prettyprint-override"><code>import numpy as np
  import pandas as pd
  
  d = np.random.rand(10,3)
  df = pd.DataFrame(d)
  df
  
            0         1         2
  0  0.740335  0.957937  0.611504
  1  0.164772  0.469355  0.310799
  2  0.666506  0.030054  0.986393
  3  0.191827  0.554556  0.707453
  4  0.278617  0.532423  0.095124
  5  0.659526  0.413681  0.588372
  6  0.285892  0.466231  0.268647
  7  0.559664  0.274913  0.618610
  8  0.572839  0.490969  0.194019
  9  0.028767  0.332626  0.290148
  
  # move the third row to top
  df.iloc[:3] = df.iloc[[2,0,1]]
  df
            0         1         2
  0  0.666506  0.030054  0.986393
  1  0.740335  0.957937  0.611504
  2  0.164772  0.469355  0.310799
  3  0.191827  0.554556  0.707453
  4  0.278617  0.532423  0.095124
  5  0.659526  0.413681  0.588372
  6  0.285892  0.466231  0.268647
  7  0.559664  0.274913  0.618610
  8  0.572839  0.490969  0.194019
  9  0.028767  0.332626  0.290148
  </code></pre>
  <p>The index is unchanged.</p>
  <p>I tried
  <code>df.index[:3] = df.index[[2,0,1]]</code> (raise error) or <code>df.index.values[:3] = df.index.values[[2,0,1]]</code>, there is no error raised but the index is still unchanged.</p>