title: Why is POSIXct converted to numeric when converting list to vector
body: <p>I have a list <code>redDressTweets</code> of <code>status</code>es. <code>status</code> is a class with a field <code>created</code>. I am trying to form a list of times in which tweets were posted. Here is how I'm trying to do it</p>
  
  <pre><code>times &lt;- unlist(lapply(redDressTweets, function(tweet) {tweet$created }))
  </code></pre>
  
  <p>The output is a vector of numbers:</p>
  
  <pre><code>[1] 1478044029 1477954062 1477909847 1477887746 1477832560 1477640940 1477640939
  [8] 1477628031 1477540826
  </code></pre>
  
  <p>But the class of <code>redDressTweets[[1]]$created</code> is <code>"POSIXct" "POSIXt"</code>.</p>
  
  <p>Why is this happening and how do I stop it from converting POSIXct to numeric?</p>