Combine rows which have same value in two columns R
<p>I have a data frame that looks like:</p>

<pre><code>       A      B    C     
1.     80     1    12    
2.     80     1    13    
3.     80     2    14    
4.     81     2    15    
5 .    81     2    16    
</code></pre>

<p>I want this:</p>

<pre><code>       A'     B'    C'     
1.     80     1    12 13   
2.     80     2    14    
3.     81     2    15 16    
</code></pre>

<p>Any suggestion package etc. ?</p>