title: Fast way to flatten a list of list while only keeping the 1st element in each sublist
body: <p>Consider the command that creates a list of list as follows:</p>
  
  <pre><code>myList &lt;- list(a = list(1:5), b = "Z", c = NA)
  </code></pre>
  
  <p>This creates something like:</p>
  
  <pre><code> $a
   $a[[1]]
   [1] 1 2 3 4 5
  
   $b
   [1] "Z"
  
   $c
   [1] NA
  </code></pre>
  
  <p>Now when I do unlist to this, </p>
  
  <pre><code>unlist(myList, recursive = FALSE)
  </code></pre>
  
  <p>I get </p>
  
  <pre><code> $a
   [1] 1 2 3 4 5
  
   $b
   [1] "Z"
  
   $c
   [1] NA
  </code></pre>
  
  <p>whereas what I am actually looking for is the first element from each sublist , i.e.</p>
  
  <pre><code> 1
   "Z"
   NA
  </code></pre>
  
  <p>Loops are very slow. No loops please.</p>