<div dir="ltr"><div class="markdown-here-wrapper" style><p style="margin:1.2em 0px!important">Hi Yue,</p>
<p style="margin:1.2em 0px!important">The call <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">(float *)xpMat->matrix()</code> 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 <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">double_bigmat</code> to a <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">float</code> 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 <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">char</code>, <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">short</code>, <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">int</code>, and <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">double</code> 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.</p>
<p style="margin:1.2em 0px!important">Regards,</p>
<p style="margin:1.2em 0px!important">Scott</p>
<div title="MDH:SGkgWXVlLDxicj48YnI+VGhlIGNhbGwgYChmbG9hdCAqKXhwTWF0LSZndDttYXRyaXgoKWAgaXMg
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dG8gYSBkb3VibGUpIGFueXdheS48YnI+PGJyPlJlZ2FyZHMsPGJyPjxicj5TY290dA==" style="height:0;width:0;max-height:0;max-width:0;overflow:hidden;font-size:0em;padding:0;margin:0"></div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On 2 June 2015 at 12:58, Yue Li <span dir="ltr"><<a href="mailto:gorillayue@gmail.com" target="_blank">gorillayue@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word">Dear List,<div><br></div><div>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.</div><div><br></div><div>For instance, I have a simple function named ‘print_bigmat’ as shown below.</div><div><br></div><div>As shown in the output, ‘double_bigmat' will save the correct values of the original matrix ‘x’ but not ‘float_bigmat’.</div><div><br></div><div><div style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono';color:rgb(0,132,0)">// [[Rcpp::export]]</div><div style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono'"><span style="color:#bb2ca2">int</span> print_bigmat(SEXP pBigMat) {</div><p style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono';min-height:19px"> <br></p><div style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono'"> XPtr<BigMatrix> xpMat(pBigMat);</div><p style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono';min-height:19px"> <br></p><div style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono'"> <span style="color:#bb2ca2">const</span> mat& double_bigmat = arma::Mat<<span style="color:#bb2ca2">double</span>>((<span style="color:#bb2ca2">double</span> *)xpMat->matrix(), xpMat->nrow(), xpMat->ncol(), <span style="color:#bb2ca2">false</span>);</div><p style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono';min-height:19px"> <br></p><div style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono'"> <span style="color:#bb2ca2">const</span> fmat& float_bigmat = arma::Mat<<span style="color:#bb2ca2">float</span>>((<span style="color:#bb2ca2">float</span> *)xpMat->matrix(), xpMat->nrow(), xpMat->ncol(), <span style="color:#bb2ca2">false</span>);</div><p style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono';min-height:19px"> <br></p><div style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono'"> Rcout << double_bigmat << endl;</div><p style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono';min-height:19px"> <br></p><div style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono'"> Rcout << float_bigmat << endl;</div><p style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono';min-height:19px"> <br></p><div style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono'"> <span style="color:#bb2ca2">return</span> <span style="color:#272ad8">0</span>;</div><div style="margin:0px;font-size:16px;font-family:'Bitstream Vera Sans Mono'">}</div></div><div><br></div><div><br></div><div>Output:</div><div><br></div><div><div>> x <- matrix(rnorm(10), nrow=2)</div><div>> x</div><div> [,1] [,2] [,3] [,4] [,5]</div><div>[1,] -0.05514382 -0.03943825 1.4145593 -0.1161918 2.3282466</div><div>[2,] -1.22023371 -0.35592125 0.7714512 0.6865120 -0.3504811</div><div>> print_bigmat(as.big.matrix(x)@address)</div><div> -0.0551 -0.0394 1.4146 -0.1162 2.3282</div><div> -1.2202 -0.3559 0.7715 0.6865 -0.3505</div><div><br></div><div> -3.3865e-14 -8.6552e+04 4.5441e-07 -5.0912e+23 -1.5184e+34</div><div> -1.3456e+00 -1.9025e+00 -1.2828e+00 -1.6780e+00 1.9268e+00</div><div><br></div><div>[1] 0</div><div>> </div></div><div><br></div><div><br></div><div>Thanks much,</div><div><div>Yue</div></div><div><br></div><div><br></div></div><br>_______________________________________________<br>
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