title: Make an array by selecting data from two sub-lists in a big list
body: <p>I need to make a three dimensional array with data in a list <code>A</code>. I am not sure if I can use <code>[]</code> directly to select data from two sub-lists in a list. As an example, I want to make an array by <code>A$aa$a</code> and <code>A$bb$a</code>. Can I select them by <code>A[[1:2]][1]</code> and make the array by the codes below?</p>
  <pre><code>A &lt;- list (aa = list(a = data.frame(matrix(1:10,10,15)),
                        b = data.frame(matrix(1:10,10,15))),
              bb = list(a = data.frame(matrix(1:10,10,15)),
                        b = data.frame(matrix(1:10,10,15))))
  
  b &lt;- lapply(A[[1:2]][1], as.matrix)
  c &lt;- c(b, recursive = TRUE)
  d &lt;- array(c, dim=c(10,15,2))
  </code></pre>