boost_1_45_0/libs/accumulators/example/main.cpp

///////////////////////////////////////////////////////////////////////////////
// main.hpp
//
//  Copyright 2005 Eric Niebler. Distributed under the Boost
//  Software License, Version 1.0. (See accompanying file
//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

#include <iostream>
#include <algorithm>
#include <boost/ref.hpp>
#include <boost/bind.hpp>
#include <boost/array.hpp>
#include <boost/foreach.hpp>
#include <boost/accumulators/accumulators.hpp>
#include <boost/accumulators/statistics.hpp>

using namespace boost;
using namespace boost::accumulators;

// Helper that uses BOOST_FOREACH to display a range of doubles
template<typename Range>
void output_range(Range const &rng)
{
    bool first = true;
    BOOST_FOREACH(double d, rng)
    {
        if(!first) std::cout << ", ";
        std::cout << d;
        first = false;
    }
    std::cout << '\n';
}

///////////////////////////////////////////////////////////////////////////////
// example1
//
//  Calculate some useful stats using accumulator_set<> and std::for_each()
//
void example1()
{
    accumulator_set<
        double
      , stats<tag::min, tag::mean(immediate), tag::sum, tag::moment<2> >
    > acc;

    boost::array<double, 4> data = {0., 1., -1., 3.14159};

    // std::for_each pushes each sample into the accumulator one at a
    // time, and returns a copy of the accumulator.
    acc = std::for_each(data.begin(), data.end(), acc);

    // The following would be equivalent, and could be more efficient
    // because it doesn't pass and return the entire accumulator set
    // by value.
    //std::for_each(data.begin(), data.end(), bind<void>(ref(acc), _1));

    std::cout << "  min""(acc)        = " << (min)(acc) << std::endl; // Extra quotes are to prevent complaints from Boost inspect tool
    std::cout << "  mean(acc)       = " << mean(acc) << std::endl;

    // since mean depends on count and sum, we can get their results, too.
    std::cout << "  count(acc)      = " << count(acc) << std::endl;
    std::cout << "  sum(acc)        = " << sum(acc) << std::endl;
    std::cout << "  moment<2>(acc)  = " << accumulators::moment<2>(acc) << std::endl;
}

///////////////////////////////////////////////////////////////////////////////
// example2
//
//  Calculate some tail statistics. This demonstrates how to specify
//  constructor and accumulator parameters. Note that the tail statistics
//  return multiple values, which are returned in an iterator_range.
//
//  It pushes data in and displays the intermediate results to demonstrate
//  how the tail statistics are updated.
void example2()
{
    // An accumulator which tracks the right tail (largest N items) and
    // some data that are covariate with them. N == 4.
    accumulator_set<
        double
      , stats<tag::tail_variate<double, tag::covariate1, right> >
    > acc(tag::tail<right>::cache_size = 4);

    acc(2.1, covariate1 = .21);
    acc(1.1, covariate1 = .11);
    acc(2.1, covariate1 = .21);
    acc(1.1, covariate1 = .11);

    std::cout << "  tail            = "; output_range(tail(acc));
    std::cout << "  tail_variate    = "; output_range(tail_variate(acc));
    std::cout << std::endl;

    acc(21.1, covariate1 = 2.11);
    acc(11.1, covariate1 = 1.11);
    acc(21.1, covariate1 = 2.11);
    acc(11.1, covariate1 = 1.11);

    std::cout << "  tail            = "; output_range(tail(acc));
    std::cout << "  tail_variate    = "; output_range(tail_variate(acc));
    std::cout << std::endl;

    acc(42.1, covariate1 = 4.21);
    acc(41.1, covariate1 = 4.11);
    acc(42.1, covariate1 = 4.21);
    acc(41.1, covariate1 = 4.11);

    std::cout << "  tail            = "; output_range(tail(acc));
    std::cout << "  tail_variate    = "; output_range(tail_variate(acc));
    std::cout << std::endl;

    acc(32.1, covariate1 = 3.21);
    acc(31.1, covariate1 = 3.11);
    acc(32.1, covariate1 = 3.21);
    acc(31.1, covariate1 = 3.11);

    std::cout << "  tail            = "; output_range(tail(acc));
    std::cout << "  tail_variate    = "; output_range(tail_variate(acc));
}

///////////////////////////////////////////////////////////////////////////////
// example3
//
//  Demonstrate how to calculate weighted statistics. This example demonstrates
//  both a simple weighted statistical calculation, and a more complicated
//  calculation where the weight statistics are calculated and stored in an
//  external weight accumulataor.
void example3()
{
    // weight == double
    double w = 1.;

    // Simple weighted calculation
    {
        // stats that depend on the weight are made external
        accumulator_set<double, stats<tag::mean>, double> acc;

        acc(0., weight = w);
        acc(1., weight = w);
        acc(-1., weight = w);
        acc(3.14159, weight = w);

        std::cout << "  mean(acc)       = " << mean(acc) << std::endl;
    }

    // Weighted calculation with an external weight accumulator
    {
        // stats that depend on the weight are made external
        accumulator_set<double, stats<tag::mean>, external<double> > acc;

        // Here's an external weight accumulator
        accumulator_set<void, stats<tag::sum_of_weights>, double> weight_acc;

        weight_acc(weight = w); acc(0., weight = w);
        weight_acc(weight = w); acc(1., weight = w);
        weight_acc(weight = w); acc(-1., weight = w);
        weight_acc(weight = w); acc(3.14159, weight = w);

        std::cout << "  mean(acc)       = " << mean(acc, weights = weight_acc) << std::endl;
    }
}

///////////////////////////////////////////////////////////////////////////////
// main
int main()
{
    std::cout << "Example 1:\n";
    example1();

    std::cout << "\nExample 2:\n";
    example2();

    std::cout << "\nExample 3:\n";
    example3();

    return 0;
}