title: Multi-level lists in R
body: <p>Do I need to initialize each level of a multi-level list in R?</p>
  
  <pre><code>l=list()
  l[["top"]]=list()
  l[["top"]][["mid"]]=list()
  l[["top"]][["mid"]][["low_key_1"]]="key_1_val"
  </code></pre>
  
  <p>or is possible to apply some auto-initialization like on perl?</p>