title: Convert list/vector of strings with date format into posix date class with R
body: <p>I have a list of strings that is in our date format and I want to convert it into a list of posix dates that I can manipulate with R, how can I do that?</p>
  
  <p>This is what I have but I end up with a list of lists:</p>
  
  <pre><code> a &lt;- c("2009.01.01 00:00:00", "2009.01.01 00:00:00")
  
  z &lt;- lapply(a,function(x){strptime(x, "%Y.%m.%d %H:%M:%S")})
  
  &gt; z &lt;- lapply(a,function(x){strptime(x, "%Y.%m.%d %H:%M:%S")})
  &gt; summary(z)
       Length Class   Mode
  [1,] 1      POSIXlt list
  [2,] 1      POSIXlt list
  </code></pre>