reference/recode_na_as.html">recode_na_as</a></span><span class="op">(</span><span class="va">airquality</span><span class="op">)</span><span class="op">)</span>
<span class="co">#&gt;   Ozone Solar.R Wind Temp Month Day</span>
<span class="co">#&gt; 1    41     190  7.4   67     5   1</span>
<span class="co">#&gt; 2    36     118  8.0   72     5   2</span>
<span class="co">#&gt; 3    12     149 12.6   74     5   3</span>
<span class="co">#&gt; 4    18     313 11.5   62     5   4</span>
<span class="co">#&g