pan> <span class="n">ts</span><span class="o">.</span><span class="n">index</span><span class="o">.</span><span class="n">to_series</span><span class="p">()</span>
    <span class="k">for</span> <span class="n">c</span> <span class="ow">in</span> <span class="n">ts</span><span class="o">.</span><span class="n">columns</span><span class="p">:</span>
        <span class="c1"># test missing values</span>
        <span class="n">miss</span> <span class="o">=</span> <span class="n">ts</span><span class="p">[</sp