title: Convert a 28 level categorical variable to matrix
body: <p>I have a data set that has one column <em>company</em>, I will do regression modelling for this dataset.</p>
  
  <p>Should I convert it using model.matrix or just assign values from 1-28 in one column.</p>
  
  <p>What is the relevance of converting it to 28 columns when <em>lm</em> function can deal with it?</p>