title: Memory exhausted trying to extract from big mcmc.list
body: <p>I have problem trying to extract a single variable from big <code>mcmc.list</code>:</p>
  <pre><code>&gt; x &lt;- outRJ$mcmc[,'avail_int']
  Error: cannot allocate vector of size 146.8 Mb
  </code></pre>
  <p>The <code>outRJ$mcmc</code> mcmc.list is big, 442 MB actually (contains data for 3 chains for like 960 variables, each 20000 iterations):</p>
  <pre><code>&gt; object.size(outRJ$mcmc)/1024/1024
  [1] 442.5508 #
  </code></pre>
  <p>But the single variable should have like 234 kB only! But the extraction of it seems to require much much more memory!</p>
  <h3>How can I extract from a big mcmc.list without requiring too much memory?</h3>