title: Clustering strings in R (is it possible?)
body: <p>I have a dataset with a column that is currently being treated as a factor with 1000+ levels. These are values for the column. I would like to clean up this data.
  Some values are strings like "-18 + 5 = -13" and "5 - 18 = -13", I would like the clustering to group these differently than say "R3no4".</p>
  
  <p>Is this possible in R? I looked at the natural language processing task view <a href="http://cran.r-project.org/web/views/NaturalLanguageProcessing.html" rel="nofollow">http://cran.r-project.org/web/views/NaturalLanguageProcessing.html</a> but I need to be pushed in the right direction.</p>
  
  <p>the dataset is from the <a href="https://pslcdatashop.web.cmu.edu/KDDCup/downloads.jsp" rel="nofollow">kdd 2010 cup</a>
  I would like to create meaningful new columns from this column to aid in creating a predictive model. for example it would be nice to know if the string contains a certain operation, or if it contains no operations and instead is describing the problem.</p>
  
  <p>my data frame looks like this:</p>
  
  <pre><code>str(data1)
  'data.frame':   809694 obs. of  19 variables:
   $ Row                        : int  1 2 3 4 5 6 7 8 9 10 ...
   $ Anon.Student.Id            : Factor w/ 574 levels "02i5jCrfQK","02ZjVTxC34",..: 7 7     7 7 7 7 7 7 7 7 ...
   $ Problem.Hierarchy          : Factor w/ 138 levels "Unit CTA1_01, Section CTA1_01-1",..: 80 80 80 80 80 80 80 80 80 80 ...
   $ Problem.Name               : Factor w/ 1084 levels "1PTB02","1PTB03",..: 377 377 378 378 378 378 378 378 378 378 ...
   $ Problem.View               : int  1 1 1 1 2 2 3 3 4 4 ...
   $ Step.Name                  : Factor w/ 187539 levels "-(-0.24444444-y) = -0.93333333",..: 116742 177541 104443 64186 58776 58892 153246 153078 45114 163923 ...
  </code></pre>
  
  <p>I'm most interested in the Step.Name feature, since it contains the greatest number of unique factor values.</p>
  
  <p>and some example values for step name:</p>
  
  <pre><code>[97170] (1+7)/4 = x                                                               
  [97171] (1-sqrt(1^2-4*2*-6))/4 = x                                                
  [97172] (1-sqrt(1^2-(-48)))/4 = x                                                 
  [97173] (1-sqrt(1-(-48)))/4 = x                                                   
  [97174] (1-sqrt(49))/4 = x                                                        
  [97175] (1-7)/4 = x                                                               
  [97176] x^2+15x+44 = 0                                                            
  [97177] a-factor-node                                                             
  [97178] b-factor-node                                                             
  [97179] c-factor-node                                                             
  [97180] num1-factor-node                                                          
  [97181] num2-factor-node                                                          
  [97182] den1-factor-node                                                          
  [97183] (-15?sqrt((-15)^2-4*1*44))/2 = x                                          
  [97184] (-15+sqrt((-15)^2-4*1*44))/2 = x                                          
  [97185] (-15+sqrt((-15)^2-176))/2 = x                                             
  [97186] (-15+sqrt(225-176))/2 = x                                                 
  [97187] (-15+sqrt(49))/2 = x                                                      
  [97188] (-15+7)/2 = x                                                             
  [97189] (-15-sqrt((-15)^2-4*1*44))/2 = x                                          
  [97190] (-15-sqrt((-15)^2-176))/2 = x                                             
  [97191] (-15-sqrt(225-176))/2 = x                                                 
  [97192] (-15-sqrt(49))/2 = x                                                      
  [97193] (-15-7)/2 = x                                                             
  [97194] 2x^2+x = 0                                                                
  [97195] a-factor-node                                                             
  [97196] b-factor-node                                                             
  [97197] c-factor-node                                                             
  [97198] num1-factor-node                                                          
  [97199] num2-factor-node                                                          
  [97200] den1-factor-node                                                          
  [97201] (-1?sqrt((-1)^2-4*2*0))/4 = x                                             
  [97202] (-1+sqrt((-1)^2-4*2*0))/4 = x                                             
  [97203] (-1+sqrt((-1)^2-0))/4 = x                                                 
  [97204] (-1+sqrt((-1)^2))/4 = x                                                   
  [97205] (-1+1)/4 = x                                                              
  [97206] (-1-sqrt((-1)^2-4*2*0))/4 = x                                             
  [97207] (-1-sqrt((-1)^2-0))/4 = x                                                 
  [97208] (-1-sqrt((-1)^2))/4 = x                                                   
  [97209] (-1-1)/4 = x                                                              
  [97210] x^2-6x = 0                                                                
  [97211] a-factor-node                                                             
  [97212] b-factor-node                                                                
  </code></pre>