Is it possible to use boost accumulators with vectors?

Question

I wanted to use boost accumulators to calculate statistics of a variable that is a vector. Is there a simple way to do this. I think it\'s not possible to use the dumbest th

Answer 1

I don't have it set up to try right now, but if all boost::accumulators need is properly defined mathematical operators, then you might be able to get away with a different vector type: http://www.boost.org/doc/libs/1_37_0/libs/numeric/ublas/doc/vector.htm

Answer 2

I've looked into your question a bit, and it seems to me that Boost.Accumulators already provides support for std::vector. Here is what I could find in a section of the user's guide :

Another example where the Numeric Operators Sub-Library is useful is when a type does not define the operator overloads required to use it for some statistical calculations. For instance, std::vector<> does not overload any arithmetic operators, yet it may be useful to use std::vector<> as a sample or variate type. The Numeric Operators Sub-Library defines the necessary operator overloads in the boost::numeric::operators namespace, which is brought into scope by the Accumulators Framework with a using directive.

Indeed, after verification, the file boost/accumulators/numeric/functional/vector.hpp does contain the necessary operators for the 'naive' solution to work.

I believe you should try :

• Including either
  • boost/accumulators/numeric/functional/vector.hpp before any other accumulators header
  • boost/accumulators/numeric/functional.hpp while defining BOOST_NUMERIC_FUNCTIONAL_STD_VECTOR_SUPPORT
• Bringing the operators into scope with a using namespace boost::numeric::operators;.

There's only one last detail left : execution will break at runtime because the initial accumulated value is default-constructed, and an assertion will occur when trying to add a vector of size n to an empty vector. For this, it seems you should initialize the accumulator with (where n is the number of elements in your vector) :

accumulator_set<std::vector<double>, stats<tag::mean> > acc(std::vector<double>(n));

I tried the following code, mean gives me a std::vector of size 2 :

int main()
{
    accumulator_set<std::vector<double>, stats<tag::mean> > acc(std::vector<double>(2));

    const std::vector<double> v1 = boost::assign::list_of(1.)(2.);
    const std::vector<double> v2 = boost::assign::list_of(2.)(3.);
    const std::vector<double> v3 = boost::assign::list_of(3.)(4.);
    acc(v1);
    acc(v2);
    acc(v3);

    const std::vector<double> &meanVector = mean(acc);
}

I believe this is what you wanted ?

Answer 3

And what about the documentation?

// The data for which we wish to calculate statistical properties:
std::vector< double > data( /* stuff */ );

// The accumulator set which will calculate the properties for us:    
accumulator_set< double, features< tag::min, tag::mean > > acc;

// Use std::for_each to accumulate the statistical properties:
acc = std::for_each( data.begin(), data.end(), acc );