EQ2EMu/EQ2/source/depends/boost_1_72_0/libs/histogram/examples/getting_started_listing_01.cpp

// Copyright 2015-2018 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)

// clang-format off

//[ getting_started_listing_01

#include <algorithm>           // std::for_each
#include <boost/format.hpp>    // only needed for printing
#include <boost/histogram.hpp> // make_histogram, regular, weight, indexed
#include <cassert>             // assert (used to test this example for correctness)
#include <functional>          // std::ref
#include <iostream>            // std::cout, std::flush
#include <sstream>             // std::ostringstream

int main() {
  using namespace boost::histogram; // strip the boost::histogram prefix

  /*
    Create a 1d-histogram with a regular axis that has 6 equidistant bins on
    the real line from -1.0 to 2.0, and label it as "x". A family of overloaded
    factory functions called `make_histogram` makes creating histograms easy.

    A regular axis is a sequence of semi-open bins. Extra under- and overflow
    bins extend the axis by default (this can be turned off).

    index    :      -1  |  0  |  1  |  2  |  3  |  4  |  5  |  6
    bin edges:  -inf  -1.0  -0.5   0.0   0.5   1.0   1.5   2.0   inf
  */
  auto h = make_histogram(axis::regular<>(6, -1.0, 2.0, "x"));

  /*
    Let's fill a histogram with data, typically this happens in a loop.

    STL algorithms are supported. std::for_each is very convenient to fill a
    histogram from an iterator range. Use std::ref in the call, if you don't
    want std::for_each to make a copy of your histogram.
  */
  auto data = {-0.5, 1.1, 0.3, 1.7};
  std::for_each(data.begin(), data.end(), std::ref(h));
  // let's fill some more values manually
  h(-1.5); // is placed in underflow bin -1
  h(-1.0); // is placed in bin 0, bin interval is semi-open
  h(2.0);  // is placed in overflow bin 6, bin interval is semi-open
  h(20.0); // is placed in overflow bin 6

  /*
    This does a weighted fill using the `weight` function as an additional
    argument. It may appear at the beginning or end of the argument list. C++
    doesn't have keyword arguments like Python, this is the next-best thing.
  */
  h(0.1, weight(1.0));

  /*
    Iterate over bins with the `indexed` range generator, which provides a
    special accessor object, that can be used to obtain the current bin index,
    and the current bin value by dereferncing (it acts like a pointer to the
    value). Using `indexed` is convenient and gives you better performance than
    looping over the histogram cells with hand-written for loops. By default,
    under- and overflow bins are skipped. Passing `coverage::all` as the
    optional second argument iterates over all bins.

    - Access the value with the dereference operator.
    - Access the current index with `index(d)` method of the accessor.
    - Access the corresponding bin interval view with `bin(d)`.

    The return type of `bin(d)` depends on the axis type (see the axis reference
    for details). It usually is a class that represents a semi-open interval.
    Edges can be accessed with methods `lower()` and `upper()`.
  */

  std::ostringstream os;
  for (auto&& x : indexed(h, coverage::all)) {
    os << boost::format("bin %2i [%4.1f, %4.1f): %i\n") 
          % x.index() % x.bin().lower() % x.bin().upper() % *x;
  }

  std::cout << os.str() << std::flush;

  assert(os.str() == "bin -1 [-inf, -1.0): 1\n"
                     "bin  0 [-1.0, -0.5): 1\n"
                     "bin  1 [-0.5, -0.0): 1\n"
                     "bin  2 [-0.0,  0.5): 2\n"
                     "bin  3 [ 0.5,  1.0): 0\n"
                     "bin  4 [ 1.0,  1.5): 1\n"
                     "bin  5 [ 1.5,  2.0): 1\n"
                     "bin  6 [ 2.0,  inf): 2\n");
}

//]