title: Trying to create treemap, getting error message about invalid column names
body: <p>My code must be pretty close, but some small thing seems to be off.</p>
  
  <pre><code>library(treemap)
  
  mydata = read.csv("C:\\path\\to\\files\\top_10.csv")
  
  products &lt;- unique(mydata$product, incomparables = FALSE)
  
  treemap(mydata, #Your data frame object
          index=products,  #A list of your categorical variables
          vSize = reportable_amount,  #This is your quantitative variable
          type="index", #Type sets the organization and color scheme of your treemap
          palette = "Reds",  #Select your color palette from the RColorBrewer presets or make your own.
          title="TreeMap of Products and Amounts", #Customize your title
          fontsize.title = 14 #Change the font size of the title
          )
  </code></pre>
  
  <p>I'm getting this error message:</p>
  
  <pre><code>Error in treemap(mydata, index = products, vSize = reportable_amount,  : 
    &lt;index&gt; contains invalid column names
  </code></pre>
  
  <p>My data set looks like this.</p>
  
  <pre><code>product asofdate    reportable_amount
  CreditFacilities    3/30/2018   29918501.83
  CreditFacilities    3/30/2018   50000000
  CreditFacilities    3/30/2018   40000000
  CreditFacilities    3/30/2018   13766666.67
  CreditFacilities    3/30/2018   75000000
  CreditFacilities    3/30/2018   40000000
  CreditFacilities    3/30/2018   9450000
  CreditFacilities    3/30/2018   91287458.38
  CreditFacilities    3/30/2018   -81498.17
  CreditFacilities    3/30/2018   50000000
  DerivativePayables  3/30/2018   -294715.28
  DerivativePayables  3/30/2018   -304222.22
  DerivativePayables  3/30/2018   -294715.28
  DerivativePayables  3/30/2018   -275701.39
  DerivativePayables  3/30/2018   -106689.44
  DerivativePayables  3/30/2018   -285208.33
  DerivativePayables  3/30/2018   -137850.69
  DerivativePayables  3/30/2018   -275701.39
  DerivativePayables  3/30/2018   -285208.33
  DerivativePayables  3/30/2018   -147357.64
  DerivativeReceivables   3/30/2018   280264.06
  DerivativeReceivables   3/30/2018   144964.17
  DerivativeReceivables   3/30/2018   309256.89
  DerivativeReceivables   3/30/2018   289928.33
  DerivativeReceivables   3/30/2018   289928.33
  DerivativeReceivables   3/30/2018   299592.61
  DerivativeReceivables   3/30/2018   140132.03
  DerivativeReceivables   3/30/2018   37698.8
  DerivativeReceivables   3/30/2018   299592.61
  DerivativeReceivables   3/30/2018   154628.44
  </code></pre>
  
  <p>I have one date, the product repeats several times, and there are 326 different records.</p>
  
  <p>I got the idea from the link below, which I thought was pretty helpful.</p>
  
  <p><a href="https://rpubs.com/brandonkopp/creating-a-treemap-in-r" rel="nofollow noreferrer">https://rpubs.com/brandonkopp/creating-a-treemap-in-r</a></p>