[Rcpp-devel] R vectorisation vs. C++ vectorisation

[Romain Francois]

clip it is, with this order:

p = clip( 0.0, p, 1.0 ) ;

which I found more natural.

For now, I implemented only a version with primitives for the first and 
last argument and sugar expression for the one in the middle, but we can 
imagine writing vector versions everywhere.

Romain

Le 21/11/12 14:22, Alexandre Bujard a écrit :
> How about clip():
>      p = clip(p, 0.0, 1.0);
>
> Great idea!!!
>
>
> On Wed, Nov 21, 2012 at 2:00 PM, Romain Francois
> <romain at r-enthusiasts.com <mailto:romain at r-enthusiasts.com>> wrote:
>
>     Le 21/11/12 13:22, Darren Cook a écrit :
>
>         I wrote:
>
>                     P.S. I don't think the sugar versions can be made
>                     any quicker, because
>                     they have to allocate intermediate vectors, and do
>                     more memory copies.
>
>
>         By "sugar versions" I meant vacc4() vs. vacc3()
>         (https://gist.github.com/__4111256
>         <https://gist.github.com/4111256>) not pmin() and friends. The
>         vacc4()
>         code looks like:
>
>             NumericVector p(age.size());
>             p = 0.25 + 0.3 * 1 / (1 - exp(0.04 * age)) + 0.1 * ily;
>             p = p * ifelse(female, 1.25, 0.75);
>             p = pmax(0,p);
>             p = pmin(1,p);
>
>         Each operation copies the whole NumericVector each time, each of
>         which
>         needs a memory allocation.
>
>
>     Nope. The NumericVector::operator=( sugar expression ) is used and
>     memory for p is allocated just once, when p is constructed with this
>     lne:
>
>       NumericVector p(age.size());
>
>     None of the "p = ..." lines allocate memory for p.
>
>     The differences in timing don't come from additional memory allocations.
>
>     Although this thread allows me to identify something that can be
>     improved in the operator=.
>
>
>         vacc3a() does the same pipeline of operations on a single
>         double, which
>         is therefore likely to be a single CPU register, and the whole of
>         vacc3a() will be inlined in vacc3().
>
>
>             Also, I'm probably goinf to add a function that does the
>             equivalent of :
>
>             pmax( b, pmin( a, x ) )
>
>             I'm thinking of naming it pminmax. Any better idea ?
>
>
>         I'd expect a function called minmax() to return two values, the
>         min and
>         max function. The "p" prefix is too subtle for me :-)
>
>         How about clip():
>              p = clip(p, 0.0, 1.0);
>
>
>
>     I like "clip".
>
>
>
>         This is such a common operation that I'm surprised R doesn't already
>         have a function like this!
>
>         Darren
>
>
>
>
>     --
>     Romain Francois
>     Professional R Enthusiast
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>


-- 
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30

R Graph Gallery: http://gallery.r-enthusiasts.com
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blog:            http://romainfrancois.blog.free.fr
|- http://bit.ly/RE6sYH : OOP with Rcpp modules
`- http://bit.ly/Thw7IK : Rcpp modules more flexible