title: Calculate average over many data frames having same format?
body: <p>I have 15 data frames that are exactly identical, but each have different values stored within each column. Each header row is exactly the same.</p>
  
  <p>Here's an example data frame, call it "A":</p>
  
  <pre><code>    Product Q1 Q2
  1 Product X 10 15
  2 Product Y 20 40
  3 Product Z 30 50
  </code></pre>
  
  <p>And here's another, call it "B":</p>
  
  <pre><code>    Product Q1 Q2
  1 Product X 12  5
  2 Product Y 25 44
  3 Product Z 32 51
  </code></pre>
  
  <p>I would like to calculate the average value across all 15 data frames. Using my two examples, the output would be a similar data frame but with averages. Something like this:</p>
  
  <pre><code>    Product   Q1   Q2
  1 Product X 11.0 10.0
  2 Product Y 22.5 42.0
  3 Product Z 31.0 50.5
  </code></pre>
  
  <p>I've searched around for a solution, but to no avail. It seems like the <code>mapply</code> function might be what I need, but I'm not sure how best to put it to use here.</p>