/a></li>
<li class="chapter" data-level="5.5.5" data-path="lesson-5.html"><a href="lesson-5.html#因子factor"><i class="fa fa-check"></i><b>5.5.5</b> 因子(factor)</a></li>
</ul></li>
<li class="chapter" data-level="5.6" data-path="lesson-5.html"><a href="lesson-5.html#数据框"><i class="fa fa-check"></i><b>5.6</b> 数据框</a>
<ul>
<li class="chapter" data-level="5.6.1" data-path="lesson-5.html"><a href="lesson-5.html#数据框的索引"><i class="fa fa-check"></i><b>5.6.1</b> 数据框的索引</a></