lass="chapter" data-level="2.1.9" data-path="r-intro.html"><a href="r-intro.html#testing-early-and-often"><i class="fa fa-check"></i><b>2.1.9</b> Testing Early and Often</a></li>
</ul></li>
<li class="chapter" data-level="2.2" data-path="r-intro.html"><a href="r-intro.html#vectors"><i class="fa fa-check"></i><b>2.2</b> Vectors</a></li>
<li class="chapter" data-level="2.3" data-path="r-intro.html"><a href="r-intro.html#matrices"><i class="fa fa-check"></i><b>2.3</b> Matrices</a></li>
<li class="chapter" data