title: Replacing values in a column where there is a match
body: <p>I'm new to R programming and I'm stuck on the example below.</p>
  
  <p>Basically I have two data sets:</p>
  
  <p>dataset1: </p>
  
  <pre><code>ID       Category        
  1        CatZZ         
  2        CatVV         
  3        CatAA  
  4        CatQQ
  </code></pre>
  
  <p>dataset2:  </p>
  
  <pre><code>ID  Category  
  1   Cat600  
  3   Cat611 
  </code></pre>
  
  <p>I'm trying to overwrite the 'category' values in dataset1 with the 'category' values in dataset2 where there is an ID match between the two data sets.</p>
  
  <p>So the outcome would look something like this:</p>
  
  <p>dataset1:  </p>
  
  <pre><code>ID  Category    
  1   Cat600  
  2   CatVV  
  3   Cat611  
  4   CatQQ  
  </code></pre>