On Thu, Sep 1, 2011 at 9:19 AM, Dirk Eddelbuettel <e...@debian.org> wrote:
>
>
> I think (but feel to free me wrong by looking at headers and code :-) that
> operator() and operator[] do the same thing.
I see a huge difference in this set of
examples ( which are painfully repetitive on many levels)
that are identical except for [] vs. (). This is true whether
or not ret appears on the RHS. Am I missing something here?
library(inline);
library(Rcpp);
library(rbenchmark);
src1<-'
int nn=as<int>(n);
NumericVector ret(nn);
for (int i=0; i<nn; i++) {
for (int j=0; j<nn; j++) {
ret[i] = ret[i]+1;
// alternately,
// ret[i] = 1;
}
};
return(ret);
'
src1a<-'
int nn=as<int>(n);
NumericVector ret(nn);
for (int i=0; i<nn; i++) {
for (int j=0; j<nn; j++) {
ret(i) = ret(i)+1;
// alternately,
// ret(i) = 1;
}
};
return(ret);
'
mysample<-cxxfunction( signature(n="numeric"), src1, plugin='Rcpp')
mysamplea<-cxxfunction( signature(n="numeric"), src1a, plugin='Rcpp')
benchmark(
bracket = mysample( 1e4),
parens = mysamplea( 1e4),
replications = 10
)
test replications elapsed relative user.self sys.self user.child sys.child
1 bracket 10 1.132 1.000000 1.13 0 0 0
2 parens 10 10.190 9.001767 10.18 0 0
> There is a noNA() wrapper for Rcpp sugar to push performance -- NA checking
> is implemented on access 'because that is how R does' (and our first task to
> reproduce numbers you'd get at the R prompt) but if you know what you are
> doing and are aware of possible pitfalls you can skip this.
Ah, so that's for sugar. Thanks.
So I *can* do linear access on a NumericMatrix, ala
myMatrix[ computed_index ], which goes in column-major order.
Curiously, I don't see any timing difference here. Now I'm
confused...
src2<-'
int index, nn=as<int>(n);
NumericMatrix ret(nn, nn);
for (int i=0; i<nn; i++) {
for (int j=0; j<nn; j++) {
index = i+j*nn;
ret[index] = ret[index] + index;
}
};
return(ret);
'
src2a<-'
int index, nn=as<int>(n);
NumericMatrix ret(nn, nn);
for (int i=0; i<nn; i++) {
for (int j=0; j<nn; j++) {
index = i+j*nn;
ret(i, j) = ret(i, j) + index;
}
};
return(ret);
'
matfil<-cxxfunction( signature(n="numeric"), src2, plugin='Rcpp')
matfila<-cxxfunction( signature(n="numeric"), src2a, plugin='Rcpp')
benchmark(
bracket = matfil( 1e4),
parens = matfila( 1e4),
replications = 10
)
test replications elapsed relative user.self sys.self user.child sys.child
1 bracket 10 17.495 1.000000 13.14 4.24 0 0
2 parens 10 17.514 1.001086 13.10 4.31 0 0
-xian
--
A man, a plan, a cat, a ham, a yak, a yam, a hat, a canal – Panama!
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