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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Greetings and Salutations,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">At this code:<o:p></o:p></span></p>
<p class="MsoNormal"> <b> Rcpp::NumericVector JJ(15); // creates a vector with 15 spaces</b><o:p></o:p></p>
<p class="MsoNormal"><b> JJ[0] = 15; // fills only the first space</b><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">You have only initiated slot 0 to 15. The remaining slots (1-14) are uninitialized at 0.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">You probably want to use:<o:p></o:p></span></p>
<p class="MsoNormal"> <b> Rcpp::IntegerVector JJ = seq_len( 10 ) ; // creates 1:10 vector<o:p></o:p></b></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Why?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-indent:.5in"><b>Z[i] <- sample(15, 1, replace = FALSE, prob = (exp(prob - deno)))</b><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">The 15 really is being converted to a vector ranging from 1:15.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Sincerely,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">JJB<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> rcpp-devel-bounces@lists.r-forge.r-project.org [mailto:rcpp-devel-bounces@lists.r-forge.r-project.org]
<b>On Behalf Of </b>Shuai Wang<br>
<b>Sent:</b> Sunday, October 18, 2015 11:13 AM<br>
<b>To:</b> rcpp-devel@lists.r-forge.r-project.org; Shuai Wang <wangshuai901@gmail.com><br>
<b>Subject:</b> [Rcpp-devel] Incorrect results from RcppArmadillo::sample<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Dear list, <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I am a newbie to rcpp and currently I am trying to translate some R code into C++ code.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">In particular, when I was trying to translate the following R code into C++ code:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"> <b>Z[i] <- sample(15, 1, replace = FALSE, prob = (exp(prob - deno)))</b><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I found some errors in my C code, which troubles me a lot. <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Let's elaborate a little bit.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I found that Rcpp does not provide a <i>sample</i> function, so I follow the instructions
<a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__gallery.rcpp.org_articles_using-2Dthe-2DRcpp-2Dbased-2Dsample-2Dimplementation_&d=BQMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=Oj62bnDE1oueLU-seL9f0p1xxu4Hvw2JDuP8BUw91c8&m=u0jDj4G8ZcHg4HCnGUSLEH17Y_2FH4CvUX-OVZ6OfcU&s=hh6uiDHmyqu_RGmNuCJSz_eLVL316VejIhtlWtDKZ4c&e=">
here</a> to use <o:p></o:p></p>
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<p class="MsoNormal"><i>RcppArmadillo::sample.</i><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">However, even though the first parameter of <i>sample</i> function in R can be a integer:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"> function (x, size, replace = FALSE, prob = NULL) <o:p></o:p></p>
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<p class="MsoNormal"> {<o:p></o:p></p>
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<p class="MsoNormal"> <b> if (length(x) == 1L && is.numeric(x) && x >= 1) {</b><o:p></o:p></p>
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<p class="MsoNormal"><b> if (missing(size)) </b><o:p></o:p></p>
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<p class="MsoNormal"><b> size <- x</b><o:p></o:p></p>
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<p class="MsoNormal"> <b> <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__sample.int&d=BQMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=Oj62bnDE1oueLU-seL9f0p1xxu4Hvw2JDuP8BUw91c8&m=u0jDj4G8ZcHg4HCnGUSLEH17Y_2FH4CvUX-OVZ6OfcU&s=iBH3eCHMnRMHQ2mwiTNPV9k72ZAypzKfwhCrOe3o0fc&e=">
sample.int</a>(x, size, replace, prob)</b><o:p></o:p></p>
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<p class="MsoNormal"> }<o:p></o:p></p>
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<p class="MsoNormal"> else {<o:p></o:p></p>
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<p class="MsoNormal"> if (missing(size)) <o:p></o:p></p>
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<p class="MsoNormal"> size <- length(x)<o:p></o:p></p>
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<p class="MsoNormal"> x[<a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__sample.int&d=BQMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=Oj62bnDE1oueLU-seL9f0p1xxu4Hvw2JDuP8BUw91c8&m=u0jDj4G8ZcHg4HCnGUSLEH17Y_2FH4CvUX-OVZ6OfcU&s=iBH3eCHMnRMHQ2mwiTNPV9k72ZAypzKfwhCrOe3o0fc&e=">sample.int</a>(length(x),
size, replace, prob)]<o:p></o:p></p>
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<p class="MsoNormal"> }<o:p></o:p></p>
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<p class="MsoNormal"> }<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I figure out that the first parameter of <i>RcppArmadillo::sample
</i>cannot be a integer, it only accepts <o:p></o:p></p>
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<p class="MsoNormal">a vector. So given my R code, I translate it into the following C code.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"> <b> Rcpp:NumericVector JJ(15);</b><o:p></o:p></p>
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<p class="MsoNormal"><b> JJ[0] = 15;</b><o:p></o:p></p>
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<p class="MsoNormal"><b> </b><o:p></o:p></p>
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<p class="MsoNormal"><b> Z[i-1] = RcppArmadillo::sample(JJ, 1, false, (exp(prob - deno)))[0];</b><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Then I found some errors in the above code, say, while in the original R code, Z[i] is a random number<b> </b><b><span style="font-size:9.5pt">between 1 and 15</span></b><span style="font-size:9.5pt">, in the above C code, Z[i-1] is
<b>either 0 or 15</b>. </span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">Am I clear? Could anyone give me some help on this issue? Thank you a lot!</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">Shuai</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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