title: plotly R: keep categorical column names, but don't plot them
body: <p><strong>With this object:</strong></p>
  
  <pre><code>fullDT &lt;-
  structure(list(QuarterAndYear = structure(1:12, .Label = c("2015 Q1", 
  "2015 Q2", "2015 Q3", "2015 Q4", "2016 Q1", "2016 Q2", "2016 Q3", 
  "2016 Q4", "2017 Q1", "2017 Q2", "2017 Q3", "2017 Q4"), class = "factor"), 
      `TRUE` = c(3, 0, 1, 0, 2, 1, 0, 1, 3, 0, 0, 0), `FALSE` = c(0, 
      0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0), OTHER = c(0, 0, 0, 0, 0, 
      0, 0, 0, 0, 0, 0, 0)), class = c("data.table", "data.frame"
  ), row.names = c(NA, -12L), sorted = "QuarterAndYear")
  </code></pre>
  
  <p><strong>I can plot a graph like this:</strong></p>
  
  <pre><code>plot_ly(fullDT,x = ~QuarterAndYear,y=0,type = "scatter",mode = "lines")%&gt;%add_trace(y = ~`TRUE`)%&gt;%add_trace(y = ~`FALSE`)%&gt;%add_trace(y = ~OTHER)%&gt;%layout(xaxis= list(type = "category"))
  </code></pre>
  
  <p>Which gives me almost everything I need. Namely, it gives me the first column category names as tick labels for the x-axis. However, the "trace 0" shows up in the legend. If I remove this:</p>
  
  <pre><code>plot_ly(fullDT,type = "scatter",mode = "lines")%&gt;%add_trace(y = ~`TRUE`)%&gt;%add_trace(y = ~`FALSE`)%&gt;%add_trace(y = ~OTHER)%&gt;%layout(xaxis= list(type = "category"))
  </code></pre>
  
  <p>the x-axis is now unlabeled.
  I'm not sure how to get both of these to work simultaneously. I could do some sort of legend magic, maybe? but I feel like theres a cleaner way. </p>
  
  <p>I've tried some layout<code>(xaxis = list(...))</code> stuff to no avail...</p>