title: R: using apply function on a list to get mean of multiple values
body: <p>I have a list that looks like this. I've split it by 'ID', resulting in about 1,400 different components of the list (each one is a different location containing multiple species observations) . </p>
  
  <pre><code>                   ID Species   2013       2008       2003
             AA 1501106      11   1751.047   1504.080   1580.337    
             AA 1501106      11   1856.224   1678.837   1592.824      
             AA 1502114      11   1766.527   1519.468   1647.180      
  </code></pre>
  
  <p>So now I know that I can select individual components and summary() will give me the mean, median, etc of each of that specific element for 2013, 2008 and 2003, but with so many components that becomes confusing to sort through</p>
  
  <p>What I would like is to be able to get the mean of every component per year (so the mean for 2013, 2008 and 2003) </p>
  
  <p>using </p>
  
  <pre><code>apply(plot_list,mean)
  </code></pre>
  
  <p>doesn't work, presumably because the list is not just one column.</p>
  
  <p>any ideas on how i can solve this?</p>