title: Draw histograms per row over multiple columns in R
body: <p>I'm using R for the analysis of my master thesis
  I have the following data frame: STOF: Student to staff ratio</p>
  
  <pre><code>    HEI.ID   X2007 X2008 X2009 X2010 X2011 X2012 
  1        OP  41.8 147.6  90.3  82.9 106.8  63.0    
  2        MO  20.0  20.8  21.1  20.9  12.6  20.6    
  3        SD  21.2  32.3  25.7  23.9  25.0  40.1    
  4        UN  51.8  39.8  19.9  20.9  21.6  22.5    
  5        WS  18.0  19.9  15.3  13.6  15.7  15.2    
  6        BF  11.5  36.9  20.0  23.2  18.2  23.8    
  7        ME  34.2  30.3  28.4  30.1  31.5  25.6    
  8        IM   7.7  18.1  20.5  14.6  17.2  17.1    
  9        OM  11.4  11.2  12.2  11.1  13.4  19.2    
  10       DC  14.3  28.7  20.1  17.0  22.3  16.2    
  11       OC  28.6  44.0  24.9  27.9  34.0  30.7    
  </code></pre>
  
  <p>Then I rank colleges using this commend</p>
  
  <pre><code>HEIrank1&lt;-(STOF[,-c(1)])
  rank1 &lt;- apply(HEIrank1,2,rank)
  
  &gt; HEIrank11
       HEI.ID X2007 X2008 X2009 X2010 X2011 X2012
  1        OP  18.0    20  20.0  20.0  20.0    20
  2        MO  14.0     9  13.0  13.5   2.0    12
  3        SD  15.0    16  17.0  16.0  16.0    19
  4        UN  20.0    18   8.0  13.5  14.0    13
  5        WS  12.0     8   4.0   7.0   6.0     8
  6        BF   6.5    17   9.5  15.0  10.0    14
  7        ME  17.0    15  19.0  19.0  17.0    15
  8        IM   2.0     6  12.0   8.0   8.5    10
  9        OM   4.5     3   2.5   3.0   3.0    11
  10       DC  11.0    14  11.0   9.0  15.0     9
  11       OC  16.0    19  16.0  18.0  19.0    17
  </code></pre>
  
  <p>I would like to draw histogram for each HEIs (for each row)?</p>