1  2      1a       4                   1     A    1a</span>
<span class="r-out co"><span class="r-pr">#&gt;</span>                         2  3      1a       5                   1     A    1a</span>
<span class="r-out co"><span class="r-pr">#&gt;</span>                      &lt;NA&gt;  4      1a       1                &lt;NA&gt;     A    1a</span>
<span class="r-out co"><span class="r-pr">#&gt;</span>                         2  5      1a       2                   1     A    1a</span>
<span class="r-out co">