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

[Romain Francois]

Le 05/06/13 15:37, Toni Giorgino a écrit :
> 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.
>
> The single-argument erase() also seems to behave unexpectedly (below).

Also fixed, in rev 4333.

> 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 <mailto:romain at r-enthusiasts.com>> wrote:
>
>     Thanks. I'll have a look.
>
>     Le 05/06/13 14:09, Toni Giorgino a écrit :
>
>         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
>
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>
>
>
>
> --
> Toni


-- 
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