Skip to content
Prev 5991 / 10988 Next
Original Raw

[Rcpp-devel] Fwd: Possible inconsistency in Rcpp vs stl in erase(iterator, iterator)

Dirk Eddelbuettel
On 5 June 2013 at 15:37, Toni Giorgino wrote:
| Dears,
| 
| thanks. In fact I've found the problem while looking for a workaround to the
| push_back() slowness (used here for convenience only). The workaround was to
| preallocate the List, then discard the unneeded portion, for which I looked
| into erase(). This was many orders of magnitude faster.

A valid alternative is using actual STL types, and converting those before
returning (which even works automagically). You can also look into Armadillo
(or Eigen) vectors.
 
| The single-argument erase() also seems to behave unexpectedly (below).

Yes, right now it looks like you found a genuine, ahem, "infelicity". 

Dirk
 
| Best
| Toni
| 
| #include <Rcpp.h>
| #include <iostream>
| 
| // [[Rcpp::export]]
| SEXP truncateTest2() {
| 
| ? using namespace std;
| ? using namespace Rcpp;
| 
| ? Rcpp::List l;
| ? std::vector<int> v;
| 
| ? for (int i=1; i<=10; i++) {
| ??? v.push_back(i);
| ??? l.push_back(i);
| ? }
| 
| ? // Attempt truncation in another way
| ? vector<int>::iterator vi=v.begin()+1;
| ? while(vi!=v.end())
| ??? vi=v.erase(vi);??? ??? // This works
| 
| ? cout << "std::vector left with " << v.size() << endl;
| 
| ? Rcpp::List::iterator li=l.begin()+1;
| ? while(li!=l.end())
| ??? li=l.erase(li);??? ??? // This doesn't
| 
| ? cout << "Rcpp::List? left with " << l.size() << endl;
| 
| ? return(R_NilValue);
| 
| }
| 
| 
| 
| 
| 
| 
| 
| On Wed, Jun 5, 2013 at 2:50 PM, Romain Francois <romain at r-enthusiasts.com>
| wrote:
| 
|     Thanks. I'll have a look.
| 
|     Le 05/06/13 14:09, Toni Giorgino a ?crit :
| 
| 
|         Dears,
| 
|         I am a newbie to Rcpp. ?I may have found an off-by-one inconsistency
|         in
|         the handling of ?List::erase(iter1,iter2) operation with respect to
|         its
|         homologous in the STL (which I suppose is intended to mimic). ?In STL,
|         iter2 can be the container's .end(); in Rcpp, the same gives an out of
|         boundary error. (See below)
| 
|         Thanks for the incredible package. Best
| 
|         Test case...
| 
|         #include <Rcpp.h>
|         #include <iostream>
| 
|         // [[Rcpp::export]]
|         SEXP truncateTest() {
|         BEGIN_RCPP
| 
|         ? ?using namespace std;
|         ? ?Rcpp::List l;
|         ? ?std::vector<int> v;
| 
|         ? ?for (int i=1; i<=10; i++) {
|         ? ? ?v.push_back(i);
|         ? ? ?l.push_back(i);
|         ? ?}
| 
|         ? ?v.erase(v.begin()+5,v.end()-1);
|         ? ?l.erase(l.begin()+5,l.end()-1); // ?
| 
|         ? ?cout << "std::vector left with " << v.size() << endl;
|         ? ?cout << "Rcpp::List ?left with " << l.size() << endl;
| 
|         END_RCPP
|         }
| 
|         /*** R
|         # ?library(Rcpp)
|         # ?sourceCpp("truncateTest.cpp")
|         # ?truncateTest()
|         # ?#prints 6 and 5
|         */
| 
| 
| 
|     --
|     Romain Francois
|     Professional R Enthusiast
|     +33(0) 6 28 91 30 30
| 
|     R Graph Gallery: http://gallery.r-enthusiasts.com
| 
|     blog: ? ? ? ? ? ?http://blog.r-enthusiasts.com
|     |- http://bit.ly/Zs97qg ?: highlight 0.4.1
|     `- http://bit.ly/10X94UM : Mobile version of the graph gallery
| 
| 
| 
| 
| 
| --
| Toni
| 
| 
| 
| 
| 
| --
| Toni
| 
| 
| 
| ----------------------------------------------------------------------
| _______________________________________________
| 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

Thread (3 messages)

Toni Giorgino Possible inconsistency in Rcpp vs stl in erase(iterator, iterator) Jun 5 Dirk Eddelbuettel Possible inconsistency in Rcpp vs stl in erase(iterator, iterator) Jun 5 Romain Francois Possible inconsistency in Rcpp vs stl in erase(iterator, iterator) Jun 5