>ts</span><span class="o">.</span><span class="n">copy</span><span class="p">()</span>
    <span class="n">cols</span> <span class="o">=</span> <span class="n">ts_out</span><span class="o">.</span><span class="n">columns</span>
    <span class="k">for</span> <span class="n">col</span> <span class="ow">in</span> <span class="n">cols</span><span class="p">:</span>
        <span class="n">id_key</span> <span class="o">=</span> <span class="kc">True</span>
        <span class="c1"># test missing values</span>
 