title: force ordering of specific columns in pandas
body: <p>I have a dataframe with many columns.</p>
  
  <pre><code>df=pd.DataFrame(data=np.random.rand(100,1000))
  </code></pre>
  
  <p>I need to have two specific column, say <code>[793]</code> and <code>[642]</code> as the first ones, while the order of the others does not matter.</p>
  
  <p>I could do </p>
  
  <pre><code>df.columns=[793,642,...the rest...]
  </code></pre>
  
  <p>However, my columns are variable, as well as the reference ones.</p>