/a>
<a class="sourceLine" id="cb11-13" data-line-number="13"><span class="co">#&gt;  4 is.na      data cleaning </span></a>
<a class="sourceLine" id="cb11-14" data-line-number="14"><span class="co">#&gt;  5 is.na      data cleaning </span></a>
<a class="sourceLine" id="cb11-15" data-line-number="15"><span class="co">#&gt;  6 ggplot     visualization </span></a>
<a class="sourceLine" id="cb11-16" data-line-number="16"><span class="co">#&gt;  7 aes        visualization </span></a>
<a class="sourceLine" id="cb