title: Patsy formula when variable has a hypthen
body: <p>I am trying to use the statsmodel linear regression functions with formulas. My sample data is coming from a Pandas data frame. I am having a slight problem with column names within the formula.  Due to the downstream processes, I have hyphens within my column names. For example:</p>
  
  <pre><code>+------+-------+-------+
  + VOLT +  B-NN + B-IDW +
  +------+-------+-------+
  </code></pre>
  
  <p>Now, one of the reasons for keeping the hyphen as it allows python to split the string for other analysis, so I have to keep it. As you can see, when I want to regress VOLT with B-NN using <code>VOLT ~ B-NN</code>, I encounter a problem as the patsy formula cannot find B. </p>
  
  <p>Is there a way to tell Patsy that <em>B-NN</em> is a variable name and not B minus NN?</p>
  
  <p>Thanks.</p>
  
  <p>BJR</p>