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<p style="margin-top:0;margin-bottom:0">dear serguei,</p>
<p style="margin-top:0;margin-bottom:0"> I have another question:</p>
<p style="margin-top:0;margin-bottom:0">If M is a matrix, M.nrow() should return the number of rows...but I encountered the following inconsistency:</p>
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<div>> M</div>
<div> x y z</div>
<div>[1,] 1 0 0</div>
<div>[2,] 4 3 0</div>
<div>[3,] 3 1 1</div>
<div>[4,] 2 90 87</div>
<div>[5,] 9 76 23</div>
<div>[6,] 5 23 13</div>
<div>> cppFunction('IntegerVector tccp5(IntegerMatrix M) { int x = M.nrow(); return x;}')</div>
<div>> tccp5(M)</div>
<div>[1] 0 0 0 0 0 0</div>
<div><br>
</div>
<div>can you please explain what is happening( I am very new to Rcpp and C++)?</div>
<div><br>
</div>
<div>very many thanks for your time and effort...</div>
<div>yours sincerely,</div>
<div>AKSHAY M KULKARNI</div>
<br>
<p></p>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Serguei Sokol <serguei.sokol@gmail.com><br>
<b>Sent:</b> Tuesday, March 20, 2018 7:26 PM<br>
<b>To:</b> akshay kulkarni; Rcpp R<br>
<b>Subject:</b> Re: [Rcpp-devel] how to reference a row of a matrix in C++ in Rcpp</font>
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<div class="PlainText">Le 20/03/2018 à 12:10, akshay kulkarni a écrit :<br>
> dear members,<br>
> <br>
> I came to know from stackoverflow that the following references a row in a matrix in C++:<br>
> <br>
> M[2] references 2nd row of the Matrix.<br>
SO is too big to check this assertion by ourself. Do you have a link?<br>
<br>
> <br>
> <br>
> I am using Rcpp to write C++ code in R.<br>
> <br>
> <br>
> However, I ended up with the following inconsistency:<br>
> <br>
> > M<br>
> x y z<br>
> [1,] 1 1 1<br>
> [2,] 2 2 2<br>
> [3,] 3 3 3<br>
> [4,] 4 4 4<br>
> [5,] 5 5 5<br>
> [6,] 6 6 6<br>
> > cppFunction('IntegerVector tccp3(IntegerMatrix M) { IntegerVector x = M[2]; return x;}')<br>
Try<br>
<br>
cppFunction('IntegerVector tccp3(IntegerMatrix M) { IntegerVector x = M(2,_); return x;}')<br>
<br>
Best,<br>
Serguei.<br>
<br>
<br>
> > tccp3(M)<br>
> [1] 0 0 0<br>
> > cppFunction('IntegerVector tccp4(IntegerMatrix M) { IntegerVector x = M[1]; return x;}')<br>
> > tccp4(M)<br>
> [1] 0 0<br>
> <br>
> tccp3 should return (3,3,3) and tccp4 should return (2,2,2). Can you please shed light on what is going on?<br>
> <br>
> very many thanks for your time and effort....<br>
> <br>
> Yours sincerely,<br>
> AKSHAY M KULKARNI<br>
> <br>
> <br>
> <br>
> _______________________________________________<br>
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