Oh nice catch! It’s not in the latest version on CRAN, but if you install
the development version from github (
devtools::install_github("kaneplusplus/bigmemory")) you will be able to
create a big matrix with a type float. You will just need to explicitly
tell R to store the data as a float, i.e. as.big.matrix(x, type="float").
Be warned though, your print code will probably segfault when you create
the arma::Mat and try to print the matrix.
On 2 June 2015 at 14:30, Yue Li <gorilla...@gmail.com> wrote: > I see. Thanks for the explanation Scott. Wish the bigmatrix will get > native float type. I found a related post here: > https://github.com/kaneplusplus/bigmemory/issues/4 > > Yue > > > > On Jun 2, 2015, at 12:27 AM, Scott Ritchie <sritchi...@gmail.com> wrote: > > Hi Yue, > > The call (float *)xpMat->matrix() is simply telling C++ to interpret the > stored memory as a float, so it’s simply breaking up the stored binary data > into float-sized chunks instead of double-sized chunks, so you get nonsense > numbers. To store as a float, you would have to cast double_bigmat to a > float type, which I believe makes a new copy of the object after casting > each value, so would defeat the purpose. Also big.matrix objects in R only > support char, short, int, and double as the underlying storage type (see > help(“big.matrix”, “bigmemory”)), so you wouldn’t be able to access the > float matrix from R as a big.matrix (without casting it back to a double) > anyway. > > Regards, > > Scott > > > On 2 June 2015 at 12:58, Yue Li <gorilla...@gmail.com> wrote: > >> Dear List, >> >> I wonder if there is a way to convert a big matrix to ‘float’ instead of >> ‘double’ within a Rcpp program. The reason for using float is mainly for >> performance improvement. >> >> For instance, I have a simple function named ‘print_bigmat’ as shown >> below. >> >> As shown in the output, ‘double_bigmat' will save the correct values of >> the original matrix ‘x’ but not ‘float_bigmat’. >> >> // [[Rcpp::export]] >> int print_bigmat(SEXP pBigMat) { >> >> XPtr<BigMatrix> xpMat(pBigMat); >> >> const mat& double_bigmat = arma::Mat<double>((double >> *)xpMat->matrix(), xpMat->nrow(), xpMat->ncol(), false); >> >> const fmat& float_bigmat = arma::Mat<float>((float >> *)xpMat->matrix(), xpMat->nrow(), xpMat->ncol(), false); >> >> Rcout << double_bigmat << endl; >> >> Rcout << float_bigmat << endl; >> >> return 0; >> } >> >> >> Output: >> >> > x <- matrix(rnorm(10), nrow=2) >> > x >> [,1] [,2] [,3] [,4] [,5] >> [1,] -0.05514382 -0.03943825 1.4145593 -0.1161918 2.3282466 >> [2,] -1.22023371 -0.35592125 0.7714512 0.6865120 -0.3504811 >> > print_bigmat(as.big.matrix(x)@address) >> -0.0551 -0.0394 1.4146 -0.1162 2.3282 >> -1.2202 -0.3559 0.7715 0.6865 -0.3505 >> >> -3.3865e-14 -8.6552e+04 4.5441e-07 -5.0912e+23 -1.5184e+34 >> -1.3456e+00 -1.9025e+00 -1.2828e+00 -1.6780e+00 1.9268e+00 >> >> [1] 0 >> > >> >> >> Thanks much, >> Yue >> >> >> >> _______________________________________________ >> Rcpp-devel mailing list >> Rcpp-devel@lists.r-forge.r-project.org >> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel >> > > >
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