nk">head</a></span><span class="op">(</span><span class="va">us_monthly</span><span class="op">)</span></span></span>
<span class="r-out co"><span class="r-pr">#&gt;</span>         date       y</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 1 2001-01-01 2676998</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 2 2001-02-01 2309464</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 3 2001-03-01 2246633</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 4 2001-