title: R: Aggregate character strings
body: <p>I have a data frame <code>ModelDF</code> having columns with numeric as well as character values like:</p>
  
  <pre><code>Quantity        Type        Mode        Company
     1            Shoe        hello        Nike
     1            Shoe        hello        Nike
     2            Jeans       hello        Levis
     3            Shoe        hello        Nike
     1            Jeans       hello        Levis
     1            Shoe        hello        Adidas
     2            Jeans       hello        Spykar
     1            Shoe        ahola        Nike
     1            Jeans       ahola        Levis
  </code></pre>
  
  <p>I have to aggregate it in this form</p>
  
  <pre><code>Quantity        Type        Mode        Company
     5            Shoe        hello        Nike
     3            jeans       hello        Levis
     1            Shoe        hello        adidas
     2            jeans       hello        Spykar
     1            Shoe        ahola        Nike
     1            jeans       ahola        Levis
  </code></pre>
  
  <p>i.e. I have to aggregate and sum Quantity if all other columns are same.</p>
  
  <p>I have tried it using <code>aggregate</code> but as it doesn't work on character values it is giving me wrong results.</p>
  
  <p>What are my options?
  Thanks</p>