title: Change decimal digits for data frame column in R
body: <p>Questions about displaying of certain numbers of digits have been posted, however, just for single values or vectors, so I hope someone can help me with this.</p>
  
  <p>I have a data frame with several columns and want to display all values in one column with two decimal digits (this column only). I have tried <code>round()</code> and <code>format()</code> and <code>options(digits)</code> but none worked on a column <code>(numerical)</code>. I wonder if there is a method to do this without going the extra way of converting the column to a vector and gluing all together again.</p>
  
  <p>Thanks a lot!</p>