title: Why does my Pandas DataFrame not display new order using `sort_values`?
body: <p>New to Pandas, so maybe I'm missing a big idea? 
  I have a Pandas DataFrame of register transactions with shape like <code>(500,4)</code>:</p>
  
  <pre><code>Time              datetime64[ns]
  Net Total                float64
  Tax                      float64
  Total Due                float64
  </code></pre>
  
  <p>I'm working through my code in a <strong>Python3 Jupyter notebook</strong>. I can't get past sorting <strong>any</strong> column. Working through the different code examples for sort, I'm not seeing the output reorder when I inspect the df. So, I've reduced the problem to trying to order just one column:</p>
  
  <pre><code>df.sort_values(by='Time')
  # OR
  df.sort_values(['Total Due'])
  # OR
  df.sort_values(['Time'], ascending=True)
  </code></pre>
  
  <p>No matter which column title, or which boolean argument I use, the displayed results never change order. </p>
  
  <p>Thinking it could be a Jupyter thing, I've previewed the results using <code>print(df)</code>, <code>df.head()</code>, and <code>HTML(df.to_html())</code> (the last example is for Jupyter notebooks). I've also rerun the whole notebook from import CSV to this code. And, I'm also new to Python3 (from 2.7), so I get stuck with that sometimes, but I don't see how that's relevant in this case.</p>
  
  <p><strong>Another post</strong> has a similar problem, <a href="https://stackoverflow.com/questions/39590055/python-pandas-dataframe-sort-values-does-not-work">Python pandas dataframe sort_values does not work</a>. In that instance, the ordering was on a column type <code>string</code>. But as you can see all of the columns here are unambiguously sortable.</p>
  
  <p>Why does my Pandas DataFrame not display new order using <code>sort_values</code>?</p>