[Rcpp-devel] RcppParallel wrong after correct

[Romain Francois]

Can you prepare a reprex ?

> Le 2 juin 2017 à 15:40, "f.krah at mailbox.org" <f.krah at mailbox.org> a écrit :
> 
> Hi all,
> 
> I wrote a function foo using RcppParallel and I am observing a bug, which I can’t figure out.
> I first wrote the function in R, then in Rcpp, then RcppParallel.
> 
> foo is doing exactly what it is supposed to do in R and Rcpp.
> However, I am observing some wired things in RcppParallel.
> 
> foo_par is running, giving almost what I want.
> 
> foo compares two matrices columnwise all pairwise combinations.
> thus we have 3 loops. 
> In the smallest step it takes two values e.g. m[c(row1, row2), 1] from the first matrix and checks if they are
> appear in 1 column in the second matrix. If they are 1 is returned, if not 0.
> 
> However, before that there is a check if one of the c(1,2) is even, then only a NA is returned. 
> Check below for this step.
> 
> The wired thing is, that this works perfectly fine the very 1st instance this case happens 
> and not any more in the thereafter examples. 
> 
> E.g: 
> 
> > foo(m1, m2)
>      [,1] [,2] [,3] [,4]
> [1,]    1    1    1    1
> [2,]    1   NA    1    0*
> [3,]    1    0*    1    0*
> 
> the 0s with * should be NA. 
> 
> 
> 
> if ( (row1 % 2 == 0) || (row2 % 2 == 0) ){
>        
>            result_matrix(count, col) = NA_REAL;
> 
>           } else { 
> 
> do the 0, 1 stuff
> }
> 
> ** count: i am using a counter for the filling of the resulting matrix (indicates the row where it should be put)
> ** col: this is from the outest loop. it loops over columns and then writes the result into the according col in the result matrix. 
> 
> 
> 
> Is this enough information?
> If someone needs to see the full function, I would prefer to send this via mail directly, since 
> this is for a publication…
> 
> I appreciate any hints!
> And I am wondering if this is coming from the parallelization itself?
> The modulo is somehow not working correctly?
> 
> Cheers, 
> Franz
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