[Rcpp-devel] Is there a way to pass references to R

Nick Matzke matzke at berkeley.edu
Sat Dec 22 01:16:45 CET 2012


Hi,

I'm working on a problem that involves calculating a very 
large, sparse transition probability matrix, P.  It takes 
significant time to run through the whole matrix, check all 
the transitions, and put in the appropriate probabilities, 
based on multiplying parameter values j, d, e, etc.

Each time I update j, or d, or e, I would rather not go 
re-process which cells of P get j, j*d, d*e, etc.  It would 
be better to just do this once, with j, d, and e each just 
referring to a memory address.  I could then update the 
values at that memory address and re-use the matrix P 
without re-building it again and again.

Currently, my script builds P via an Rcpp function, then 
passes it to R, where it gets used (with the values 
calculated) a few hundred times (via another Rcpp function); 
then j, d, and e are updated and I have to re-calculate P.

So, my question is, is there a way to make P, currently a 
vector of float vectors, into a vector of float pointers, 
which can be passed to R and then back to Rcpp?  Or is this 
just ridiculous?

Cheers,
Nick


-- 
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Nicholas J. Matzke
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