span>(<span class='kw'>group</span> <span class='kw'>=</span> <span class='st'>'grp1'</span>)</div><div class='output co'>#&gt; <span class='message'>pad applied on the interval: month</span></div><div class='output co'>#&gt;    grp1 grp2  y       date
#&gt; 1     A    a 18 2016-06-01
#&gt; 2     A    b 13 2016-06-01
#&gt; 3     A &lt;NA&gt; NA 2016-07-01
#&gt; 4     A &lt;NA&gt; NA 2016-08-01
#&gt; 5     A &lt;NA&gt; NA 2016-09-01
#&gt; 6     A &lt;NA&gt; NA 2016-10-01
#&gt; 7     A    a 10 2016-11-01
#&gt