title: 2-Dimensional List in R
body: <p>I would like a "2-dimensional list" where entry (i, j) stores a vector/matrix of unknown size. Something like</p>
  
  <pre><code>my2Dlist[i,j] &lt;- runif(k)
  </code></pre>
  
  <p>where <code>k</code> varies with <code>i</code> and <code>j</code>. What is the data structure I am looking for?</p>
  
  <p>Thank you.</p>