Thanks a lot Scott! That works!
> On Jun 2, 2015, at 12:39 AM, Scott Ritchie <sritchi...@gmail.com> wrote:
>
> 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
> <mailto: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
> <https://github.com/kaneplusplus/bigmemory/issues/4>
>
> Yue
>
>
>
>> On Jun 2, 2015, at 12:27 AM, Scott Ritchie <sritchi...@gmail.com
>> <mailto: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
>> <mailto: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
>>
>>
>>
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>
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