title: Categorical treemap in R does not show all the categories
body: <p>I was playing with treemaps in R and when I try categorical treemap, the treemap shows only one category. I wanted to reproduce treemap <a href="https://onlinehelp.tableau.com/current/pro/desktop/en-us/buildexamples_treemap.html" rel="nofollow noreferrer">examples</a> in Tableau but the categorical example is not giving me a correct treemap. The data is public and it is from Tableau website. It can be downloaded from <a href="https://community.tableau.com/servlet/JiveServlet/download/351988-57774/Sample%20-%20Superstore.xls" rel="nofollow noreferrer">here</a>.</p>
  
  <p>If I want to color the rectangles by a numeric column, it works fine.</p>
  
  <pre><code>library(readxl)
  library(dplyr)
  Sample_Superstore &lt;- read_excel("Sample_Superstore.xls")
  grouped=Sample_Superstore%&gt;%select(`Sub-Category`,Sales,`Ship Mode`)%&gt;%
             group_by(`Sub-Category`,`Ship Mode`)%&gt;%summarise(Total_Sales=sum(Sales))
  </code></pre>
  
  <h2>Numeric column for coloring (works fine!)</h2>
  
  <pre><code>treemap(grouped, 
   index="Sub-Category", 
   vSize="Total_Sales", 
   vColor="Total_Sales",
   type="value",
   title = "",
   palette="BuGn", #"Blues" 
   border.col ="white"
  )
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/wZqOp.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wZqOp.png" alt="enter image description here"></a></p>
  
  <h3>Using categorical variable for coloring (not working)</h3>
  
  <p>It shows only one category but my data has four categories.</p>
  
  <pre><code>treemap(grouped, 
   index="Sub-Category", 
   vSize="Total_Sales",  
   vColor="Ship Mode",
   type="categorical"
  )
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/8o4nK.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8o4nK.png" alt="enter image description here"></a></p>