ceph/src/boost/libs/histogram/examples/guide_custom_accumulators_1.cpp

   1 // Copyright 2018 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_1
   8
   9 #include <boost/format.hpp>
  10 #include <boost/histogram.hpp>
  11 #include <cassert>
  12 #include <iostream>
  13 #include <sstream>
  14
  15 int main() {
  16   using namespace boost::histogram;
  17   using mean = accumulators::mean<>;
  18
  19   // Create a 1D-profile, which computes the mean of samples in each bin.
  20   auto h = make_histogram_with(dense_storage<mean>(), axis::integer<>(0, 2));
  21   // The factory function `make_profile` is provided as a shorthand for this, so this is
  22   // equivalent to the previous line: auto h = make_profile(axis::integer<>(0, 2));
  23
  24   // An argument marked as `sample` is passed to the accumulator.
  25   h(0, sample(1)); // sample goes to first cell
  26   h(0, sample(2)); // sample goes to first cell
  27   h(1, sample(3)); // sample goes to second cell
  28   h(1, sample(4)); // sample goes to second cell
  29
  30   std::ostringstream os;
  31   for (auto&& x : indexed(h)) {
  32     // Accumulators usually have methods to access their state. Use the arrow
  33     // operator to access them. Here, `count()` gives the number of samples,
  34     // `value()` the mean, and `variance()` the variance estimate of the mean.
  35     os << boost::format("index %i count %i mean %.1f variance %.1f\n") % x.index() %
  36               x->count() % x->value() % x->variance();
  37   }
  38   std::cout << os.str() << std::flush;
  39   assert(os.str() == "index 0 count 2 mean 1.5 variance 0.5\n"
  40                      "index 1 count 2 mean 3.5 variance 0.5\n");
  41 }
  42
  43 //]