ceph/src/boost/libs/histogram/examples/guide_custom_accumulators_3.cpp

   1 // Copyright 2019 Hans Dembinski
   2 //
   3 // Distributed under the Boost Software License, Version 1.0.
   4 // (See accompanying file LICENSE_1_0.txt
   5 // or copy at http://www.boost.org/LICENSE_1_0.txt)
   6
   7 //[ guide_custom_accumulators_3
   8
   9 #include <boost/format.hpp>
  10 #include <boost/histogram.hpp>
  11 #include <iostream>
  12 #include <sstream>
  13
  14 int main() {
  15   using namespace boost::histogram;
  16
  17   // Accumulator accepts two samples and an optional weight and computes the mean of each.
  18   struct multi_mean {
  19     accumulators::mean<> mx, my;
  20
  21     // called when no weight is passed
  22     void operator()(double x, double y) {
  23       mx(x);
  24       my(y);
  25     }
  26
  27     // called when a weight is passed
  28     void operator()(weight_type<double> w, double x, double y) {
  29       mx(w, x);
  30       my(w, y);
  31     }
  32   };
  33   // Note: The implementation can be made more efficient by sharing the sum of weights.
  34
  35   // Create a 1D histogram that uses the custom accumulator.
  36   auto h = make_histogram_with(dense_storage<multi_mean>(), axis::integer<>(0, 2));
  37   h(0, sample(1, 2));            // samples go to first cell
  38   h(0, sample(3, 4));            // samples go to first cell
  39   h(1, sample(5, 6), weight(2)); // samples go to second cell
  40   h(1, sample(7, 8), weight(3)); // samples go to second cell
  41
  42   std::ostringstream os;
  43   for (auto&& bin : indexed(h)) {
  44     os << boost::format("index %i mean-x %.1f mean-y %.1f\n") % bin.index() %
  45               bin->mx.value() % bin->my.value();
  46   }
  47   std::cout << os.str() << std::flush;
  48   assert(os.str() == "index 0 mean-x 2.0 mean-y 3.0\n"
  49                      "index 1 mean-x 6.2 mean-y 7.2\n");
  50 }
  51
  52 //]