Message-ID: <e7654112-d255-d971-7351-cc9c53e4947c@gmail.com>
Date: 2018-03-20T13:56:51Z
From: Serguei Sokol
Subject: [Rcpp-devel] how to reference a row of a matrix in C++ in Rcpp
In-Reply-To: <SL2P216MB0091A7BC02329005565404B6C8AB0@SL2P216MB0091.KORP216.PROD.OUTLOOK.COM>
Le 20/03/2018 ? 12:10, akshay kulkarni a ?crit?:
> dear members,
>
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?I came to know from stackoverflow that the following references a row in a?matrix in C++:
>
> M[2] references 2nd row of the Matrix.
SO is too big to check this assertion by ourself. Do you have a link?
>
>
> I am using Rcpp to write C++ code in R.
>
>
> However, I ended up with the following inconsistency:
>
> > M
> ? ? ?x y z
> [1,] 1 1 1
> [2,] 2 2 2
> [3,] 3 3 3
> [4,] 4 4 4
> [5,] 5 5 5
> [6,] 6 6 6
> > cppFunction('IntegerVector tccp3(IntegerMatrix M) { IntegerVector x = M[2]; return x;}')
Try
cppFunction('IntegerVector tccp3(IntegerMatrix M) { IntegerVector x = M(2,_); return x;}')
Best,
Serguei.
> > tccp3(M)
> [1] 0 0 0
> > cppFunction('IntegerVector tccp4(IntegerMatrix M) { IntegerVector x = M[1]; return x;}')
> > tccp4(M)
> [1] 0 0
>
> tccp3?should return (3,3,3) and tccp4 should return? (2,2,2). Can you please shed light on what is going on?
>
> very many thanks for your time and effort....
>
> Yours sincerely,
> AKSHAY M KULKARNI
>
>
>
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