title: values don't match level in R
body: <p>a few columns of a given data frame are factor level vectors, take one of them as example:</p>
  
  <pre><code>[4661] 12.7          13.2          10.1          12.3         
  [4665] Not Available 12.7          Not Available Not Available
  [4669] Not Available Not Available Not Available 11.1         
  [4673] 9.9           9             Not Available 9.7          
  [4677] 8.9           10.1          11.7          13           
  [4681] Not Available 11.5          Not Available Not Available
  [4685] 12.3          11.2          Not Available 11.1         
  [4689] 10.4          Not Available Not Available Not Available
  [4693] 11.5          Not Available Not Available Not Available
  [4697] Not Available Not Available 12            Not Available
  [4701] Not Available Not Available Not Available Not Available
  [4705] Not Available Not Available
  106 Levels: 10 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 ... Not Available
  </code></pre>
  
  <p>I find it annoying that it keeps saying the 106 levels start from 10 then 10.1, but in fact there are many values below 10, as shown in the above list.</p>
  
  <p>How do I fix this, and have levels automatically match all values? Thanks. </p>