title: Numeric data frame columns order incorrectly as string
body: <p>I have some hospital data in a dataframe, read in from a csv. I tried to order the dataframe by a user-defined column <code>col</code> and then by the hospital's name like so:</p>
  
  <pre><code>col &lt;- 'Hospital.30.Day.Death..Mortality..Rates.from.Pneumonia'
  hospitals.sorted &lt;- hospitals[order(hospitals[,col], hospitals$Hospital.Name),]
  </code></pre>
  
  <p>But I think I'm missing something; it seems to sort <code>col</code> like strings:</p>
  
  <pre><code>&gt; hospitals.sorted
  ... # so far so good # ...
  2749                                                   10.0
  2831                                                   10.0
  2891                                                   10.0
  2837                                                   10.1
  2824                                                   10.1
  2774                                                   10.1
  ... # not so good # ...
  2856                                                   15.7
  2834                                                   15.9
  2797                                                   16.0
  2835                                                    7.4
  2850                                                    7.7
  2789                                                    8.1
  ... # there are some non-numeric values at the very bottom # ...
  2806                                                    9.9
  2867                                                    9.9
  2884                                                    9.9
  2808                                          Not Available
  2913                                          Not Available
  2911                                          Not Available
  </code></pre>
  
  <p>Just to confirm the column is in fact numeric:</p>
  
  <pre><code>&gt; sapply(hospitals, mode)
  Hospital.30.Day.Death..Mortality..Rates.from.Pneumonia 
  "numeric" 
  Hospital.Name 
  "numeric"
  </code></pre>
  
  <p>I don't know why <code>Hospital.Name</code> is numeric when it's clearly not.</p>
  
  <p>Other things I tried to no avail: </p>
  
  <ul>
  <li>using <code>as.numeric(hospitals[,col])</code> inside of <code>order</code></li>
  <li>removing the "Not Available" values before sorting</li>
  </ul>
  
  <p>I may be missing something fundamental. Halp!</p>