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
<rom...@r-enthusiasts.com <mailto:rom...@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
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