[Rcpp-devel] RcppParallel with string or char?

brian knaus briank.lists at gmail.com
Wed Feb 28 17:18:35 CET 2018

Thanks Dirk! I think that does make sense. I'll work on trying to implement
it. I don't think I'll get to it today, but I'll try to post back to the
group if I arrive at a solution.


On Tue, Feb 27, 2018 at 6:58 PM, Dirk Eddelbuettel <edd at debian.org> wrote:

> On 27 February 2018 at 18:38, brian knaus wrote:
> | Thanks for the suggestion! Unfortunately, I don't follow you. This is
> | likely because this is my first attempt at parallel code outside of
> one-off
> | mclapply(). My hope is to use this in a package on CRAN, so I'd like
> | something more portable than mclapply().
> |
> | My understanding is that we need to work with 'thread safe' data
> | structures. For example, in the worker in (
> | http://gallery.rcpp.org/articles/parallel-matrix-transform/)
> | RMatrix<double> is used for input and output matrices. And part of the
> | point of RMatrix and RVector are to provide these 'thread safe' data
> | structures so the rest of us do not need to learn the details of their
> | complexities. When you say I could try using std::vector<std::string> do
> | you mean as a substitute for RMatrix in the worker? Or perhaps
> | std::vector<std::vector<std::string>> as a substitute for RMatrix?
> RMatrix (and RVector) exist because we cannot use Rcpp::NumericMatrix (and
> Rcpp::NumericVector) as those are "proxy objects" which reuse the
> R-allocated
> memory. That is not thread safe as R may have a gc event.
> So converting your R text objects into std::vector<std::string> is also
> thread-safe as it provides a distinct copy. Which is why I suggested it
> earlier.
> You said you had string data, so you likely need something just like
> std::list<std::string> or std::vector<std::string> anyway.
> Does that make sense?   One word of caution, though:  RcppParallel and
> friends are user-friendly compared to doing it by hand using OpenMP etc,
> but
> not quite as easy as mlapply.  Maybe just cooking up a simpler C++ based
> package and have that used on the parallel instances governed by mclapply?
> Dirk
> --
> http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org
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