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- // Copyright 2019 Hans Dembinski
- //
- // 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)
- //[ guide_custom_accumulators_3
- #include <boost/format.hpp>
- #include <boost/histogram.hpp>
- #include <iostream>
- #include <sstream>
- int main() {
- using namespace boost::histogram;
- // Accumulator accepts two samples and an optional weight and computes the mean of each.
- struct multi_mean {
- accumulators::mean<> mx, my;
- // called when no weight is passed
- void operator()(double x, double y) {
- mx(x);
- my(y);
- }
- // called when a weight is passed
- void operator()(weight_type<double> w, double x, double y) {
- mx(w, x);
- my(w, y);
- }
- };
- // Note: The implementation can be made more efficient by sharing the sum of weights.
- // Create a 1D histogram that uses the custom accumulator.
- auto h = make_histogram_with(dense_storage<multi_mean>(), axis::integer<>(0, 2));
- h(0, sample(1, 2)); // samples go to first cell
- h(0, sample(3, 4)); // samples go to first cell
- h(1, sample(5, 6), weight(2)); // samples go to second cell
- h(1, sample(7, 8), weight(3)); // samples go to second cell
- std::ostringstream os;
- for (auto&& bin : indexed(h)) {
- os << boost::format("index %i mean-x %.1f mean-y %.1f\n") % bin.index() %
- bin->mx.value() % bin->my.value();
- }
- std::cout << os.str() << std::flush;
- assert(os.str() == "index 0 mean-x 2.0 mean-y 3.0\n"
- "index 1 mean-x 6.2 mean-y 7.2\n");
- }
- //]
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