span class="r-pr">#&gt;</span> 20                                  &lt;NA&gt;</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 21                                  &lt;NA&gt;</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 22                                  &lt;NA&gt;</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 23                                  &lt;NA&gt;</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 24                                  &lt;NA&gt