title: Add a new column between other dataframe columns
body: <p>I want to add a new column with "NA"s in my dataframe:</p>
  
  <pre><code>     A       B
  1    14379  32094
  2   151884  174367
  3   438422  449382
  </code></pre>
  
  <p>But I need it to be located between col. A and B, like this:</p>
  
  <pre><code>     A       C      B
  1    14379   NA    32094
  2   151884   NA    174367
  3   438422   NA    449382
  </code></pre>
  
  <p>I know how to add col. C after col. B, but that is not helpful to me... Anyone know how to do it? </p>