title: merge the rows in R with the same row name concatenating the content in the column
body: <p>I need help merging the rows with the same name by concatenating the content in one of the columns. For example, in my dataframe,df, the rows with the same name match completely across the columns except in col 3. I want to merge the rows with the same rowname and concatenate the contents in col3 separated by a comma and get the result as shown below. Thank you for your help.</p>
  
  <pre><code>df
  
  rowname  col1    col2  col3 
  pat      122       A      T
  bus      222       G      C
  pat      122       A      G
  
  
  result
  
  rowname  col1    col2  col3 
  pat      122       A      T,G
  bus      222       G      C
  </code></pre>