an class="r-pr">#&gt;</span> 'data.frame':	8 obs. of  3 variables:</span>
<span class="r-out co"><span class="r-pr">#&gt;</span>  $ variable   : Factor w/ 8 levels "chl","dox","ext",..: 1 2 7 3 6 8 5 4</span>
<span class="r-out co"><span class="r-pr">#&gt;</span>  $ description: chr  "chlorophyll a" "dissolved oxygen" "suspended particulate matter" "extinction coefficient" ...</span>
<span class="r-out co"><span class="r-pr">#&gt;</span>  $ units      : chr  "mg/m3" "mg/L" "mg/L" "1/m" ...</span>
<span clas