title: Combine multiple categorical variables in one dummy variable
body: <p>I have 3 categorical variables</p>
  
  <pre><code>agegroup{&lt;20,20-30,&gt;03}    
  disease.level{0,1,2},  
  performance{&lt;60, &gt;=60}
  </code></pre>
  
  <p>and I would like to combine them into one dummy variable with 3x3x2 levels. Is there any fast way to do this? My original datasets has about 10 variables with multiple levels in each.</p>
  
  <p>Basically I am asking for the exact opposite of this question
  <a href="https://stackoverflow.com/questions/3384506/create-new-dummy-variable-columns-from-categorical-variable">Create new dummy variable columns from categorical variable</a></p>
  
  <p>Thanks a lot
  EC</p>