title: R Markdown: my code runs on the console, but not when I try to knit to HTML
body: <p>I am running the following code (referencing a data frame in my Global Environment):</p>
  
  <pre><code>schedule_sort_1 &lt;- group_by(FileName, Date)  
  schedule_table_1 &lt;- summarize(schedule_sort_1, Run_Time_hrs = sum(as.numeric(Interval_s))/3600, Start_Time = Time[1], End_Time = Time[length(Time)], Mean_Outdoor_Temp = mean(Outside.Air.Temp))  
  kable(schedule_table_1, digits = 3, align = "c")
  </code></pre>
  
  <p>When I test using the "Run Current Chunk" button, the table appears as expected; however, when I then try to knit the document, I get the following error:</p>
  
  <pre><code>Error in group_by_(.data, .dots = lazyeval::lazy_dots(...), add=add) : object 'FileName' not found Calls: &lt;Anonymous&gt; ...withVisible -&gt; eval -&gt; eval -&gt; group_by -&gt; group_by_ Execution halted
  </code></pre>
  
  <p>Any tips would be appreciate...thx</p>