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

   1 // Copyright 2015-2018 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_storage
   8
   9 #include <algorithm> // std::for_each
  10 #include <array>
  11 #include <boost/histogram.hpp>
  12 #include <boost/histogram/algorithm/sum.hpp>
  13 #include <functional> // std::ref
  14 #include <unordered_map>
  15 #include <vector>
  16
  17 int main() {
  18   using namespace boost::histogram;
  19   const auto axis = axis::regular<>(10, 0.0, 1.0);
  20
  21   auto data = {0.1, 0.3, 0.2, 0.7};
  22
  23   // Create static histogram with vector<int> as counter storage, you can use
  24   // other arithmetic types as counters, e.g. double.
  25   auto h1 = make_histogram_with(std::vector<int>(), axis);
  26   std::for_each(data.begin(), data.end(), std::ref(h1));
  27   assert(algorithm::sum(h1) == 4);
  28
  29   // Create static histogram with array<int, N> as counter storage which is
  30   // allocated completely on the stack (this is very fast). N may be larger than
  31   // the actual number of bins used; an exception is raised if N is too small to
  32   // hold all bins.
  33   auto h2 = make_histogram_with(std::array<int, 12>(), axis);
  34   std::for_each(data.begin(), data.end(), std::ref(h2));
  35   assert(algorithm::sum(h2) == 4);
  36
  37   // Create static histogram with unordered_map as counter storage; this
  38   // generates a sparse histogram where only memory is allocated for bins that
  39   // are non-zero. This sounds like a good idea for high-dimensional histograms,
  40   // but maps come with a memory and run-time overhead. The default_storage
  41   // usually performs better in high dimensions.
  42   auto h3 = make_histogram_with(std::unordered_map<std::size_t, int>(), axis);
  43   std::for_each(data.begin(), data.end(), std::ref(h3));
  44   assert(algorithm::sum(h3) == 4);
  45 }
  46
  47 //]