[Rcpp-devel] regular expression in Rcpp

[Dirk Eddelbuettel]

On 13 January 2015 at 01:27, Mark Leeds wrote:
| Hi All: I was trying to do something with regular expressions in Rcpp so I
| piggy backed
| heavily off of Dirk's boost.regex example in the Rcpp Gallery where he takes
| streams of digits and checks them for machine and human readability.
| 
| My problem is actually pretty different and simpler. Essentially, if a
| character string ends in "rhofixed" or "norhofixed", then that part of the
| character string should be removed. The R code below illiustrates what I'm
| trying to do.
| 
| But, when I write the Rcpp code to do the same thing and  set Sys.setenv
| ("PKG_LIBS"="-lboost_regex"), I don't get the same result. I don't know if 
| it's due to the regex engine being different in boost or I could be doing

Yes it is indeed different. Boost regex are their own thing. Use its
documentation. 

Alternatively, you could try linking to the Perl or POSIX ones which R
supports.  I have no ready-made example though...

Dirk

| something else wrong. Thanks for any help.
| 
| =====================================================================
| # R CODE TO ILLUSTRATE WHAT I WANT
| =====================================================================
| 
| s <- c("lngimbintrhofixed","lngimbnointnorhofixed","test")
| result <- sub("(no)?rhofixed$","",s)
| print(result)
| 
|  print(result)
| [1] "lngimbint"   "lngimbnoint" "test"      
| 
| #=====================================================================
| Rcpp CODE ATTEMPT HEAVILY BASED OFF DIRK"S EXAMPLE
| #=====================================================================
| 
| #include <Rcpp.h>
| #include <string>
| #include <boost/regex.hpp>
| 
| using namespace Rcpp;
| using namespace std;
| 
| bool validate_modelstring(const std::string& s) {
|   static const boost::regex e("^(.*)((no)?rhofixed)$");
|      return(boost::regex_match(s, e));
| }
| 
| const std::string model_format("\\1");
| const boost::regex e("\\A^(.*)((no)?rhofixed)$\\z");
| 
| std::string filtered_rhopart(const std::string& s) {
|      return boost::regex_replace(s, e, model_format, boost::match_default |
| boost::format_sed);
| }
| 
| // [[Rcpp::export]]
| Rcpp::DataFrame regexTest(std::vector<std::string> s) {
|        
|      int n = s.size();   
|      std::vector<bool> valid(n);
|      std::vector<string> outmodel(n);
|    
|      for (int i=0; i<n; i++) {
|           valid[i]  = validate_modelstring(s[i]);
|           if (valid[i]) {
|           outmodel[i] = filtered_rhopart(s[i]);
|      } else {
|         outmodel[i] = s[i];
|      }        
|      }
| 
|      return Rcpp::DataFrame::create(Rcpp::Named("input") = s,
|                     Rcpp::Named("valid") = valid,
|                     Rcpp::Named("output") = outmodel);
| }
| 
| /*** R
| s <- c("lngimbintrhofixed","lngimbnointnorhofixed","test")
| regexTest(s)
| */
| 
| 
| 
| 
| 
| 
| 
| 
| 
| _______________________________________________
| Rcpp-devel mailing list
| Rcpp-devel at lists.r-forge.r-project.org
| https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel

-- 
http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org