title: How to split a list of data.frame and apply a function to one column?
body: <p>I have a small question about apply functions.
  For example I have:</p>
  
  <pre><code>l &lt;- list(a = data.frame(A1=rep(10,5),B1=c(1,1,1,2,2),C1=c(5,10,20,7,30)),
            b = data.frame(A1=rep(20,5),B1=c(3,3,4,4,4),C1=c(3,5,10,20,30)))
  </code></pre>
  
  <p>I want to find a minimum C1 for each B1. The result should be </p>
  
  <pre><code>$a
    A1 B1 C1
    10  1  5
    10  2  7
  
  $b
    A1 B1 C1
    20  3  3
    20  4  10
  </code></pre>
  
  <p>I know how to do it with 'for', but it have to be a easier way with 'lapply', but I couldn't make it works.</p>
  
  <p>Please help</p>