histogram/examples/guide_custom_modified_axis.cpp

//[ guide_custom_modified_axis

#include <boost/histogram.hpp>
#include <iostream>

namespace bh = boost::histogram;

// custom axis, which adapts builtin integer axis
struct custom_axis : public bh::axis::integer<> {
  using value_type = const char*; // type that is fed to the axis

  using integer::integer; // inherit ctors of base

  // the customization point
  // - accept const char* and convert to int
  // - then call index method of base class
  int operator()(value_type s) const { return integer::operator()(std::atoi(s)); }
};

int main() {
  auto h = bh::make_histogram(custom_axis(0, 3));
  h("-10");
  h("0");
  h("1");
  h("9");

  for (auto xi : h.axis()) {
    std::cout << "bin " << xi.idx() << " [" << xi.lower() << ", "
              << xi.upper() << ") " << h.at(xi) << std::endl;
  }

  /* prints:
      bin 0 [0, 1) 1
      bin 1 [1, 2] 1
      bin 2 [2, 3] 0
  */
}

//]