title: Concatenating all rows within a group using dplyr
body: <p>Suppose I have a dataframe like this:</p>
  
  <pre><code>hand_id card_id card_name card_class
  A       1       p          alpha
  A       2       q          beta
  A       3       r          theta
  B       2       q          beta
  B       3       r          theta
  B       4       s          gamma
  C       1       p          alpha
  C       2       q          beta 
  </code></pre>
  
  <p>I would like to concatenate the card_id, card_name, and card_class into one single row per hand level A, B, C. So the result would look something like this:</p>
  
  <pre><code>hand_id  combo_1  combo_2  combo_3
  A        1-2-3    p-q-r    alpha-beta-theta
  B        2-3-4    q-r-s    beta-theta-gamma
  ....
  </code></pre>
  
  <p>I attempted to do this using group_by and mutate, but I can't seem to get it to work</p>
  
  <pre><code>    data &lt;- read_csv('data.csv')
      byHand &lt;- group_by(data, hand_id) %&gt;%
        mutate(combo_1 = paste(card_id), 
               combo_2 = paste(card_name),
               combo_3 = paste(card_class))
  </code></pre>
  
  <p>Thank you for your help. </p>