ceph/src/boost/libs/histogram/examples/getting_started_listing_01.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 // clang-format off
   8
   9 //[ getting_started_listing_01
  10
  11 #include <algorithm>           // std::for_each
  12 #include <boost/format.hpp>    // only needed for printing
  13 #include <boost/histogram.hpp> // make_histogram, regular, weight, indexed
  14 #include <cassert>             // assert (used to test this example for correctness)
  15 #include <functional>          // std::ref
  16 #include <iostream>            // std::cout, std::flush
  17 #include <sstream>             // std::ostringstream
  18
  19 int main() {
  20   using namespace boost::histogram; // strip the boost::histogram prefix
  21
  22   /*
  23     Create a 1d-histogram with a regular axis that has 6 equidistant bins on
  24     the real line from -1.0 to 2.0, and label it as "x". A family of overloaded
  25     factory functions called `make_histogram` makes creating histograms easy.
  26
  27     A regular axis is a sequence of semi-open bins. Extra under- and overflow
  28     bins extend the axis by default (this can be turned off).
  29
  30     index    :      -1  |  0  |  1  |  2  |  3  |  4  |  5  |  6
  31     bin edges:  -inf  -1.0  -0.5   0.0   0.5   1.0   1.5   2.0   inf
  32   */
  33   auto h = make_histogram(axis::regular<>(6, -1.0, 2.0, "x"));
  34
  35   /*
  36     Let's fill a histogram with data, typically this happens in a loop.
  37
  38     STL algorithms are supported. std::for_each is very convenient to fill a
  39     histogram from an iterator range. Use std::ref in the call, if you don't
  40     want std::for_each to make a copy of your histogram.
  41   */
  42   auto data = {-0.5, 1.1, 0.3, 1.7};
  43   std::for_each(data.begin(), data.end(), std::ref(h));
  44   // let's fill some more values manually
  45   h(-1.5); // is placed in underflow bin -1
  46   h(-1.0); // is placed in bin 0, bin interval is semi-open
  47   h(2.0);  // is placed in overflow bin 6, bin interval is semi-open
  48   h(20.0); // is placed in overflow bin 6
  49
  50   /*
  51     This does a weighted fill using the `weight` function as an additional
  52     argument. It may appear at the beginning or end of the argument list. C++
  53     doesn't have keyword arguments like Python, this is the next-best thing.
  54   */
  55   h(0.1, weight(1.0));
  56
  57   /*
  58     Iterate over bins with the `indexed` range generator, which provides a
  59     special accessor object, that can be used to obtain the current bin index,
  60     and the current bin value by dereferncing (it acts like a pointer to the
  61     value). Using `indexed` is convenient and gives you better performance than
  62     looping over the histogram cells with hand-written for loops. By default,
  63     under- and overflow bins are skipped. Passing `coverage::all` as the
  64     optional second argument iterates over all bins.
  65
  66     - Access the value with the dereference operator.
  67     - Access the current index with `index(d)` method of the accessor.
  68     - Access the corresponding bin interval view with `bin(d)`.
  69
  70     The return type of `bin(d)` depends on the axis type (see the axis reference
  71     for details). It usually is a class that represents a semi-open interval.
  72     Edges can be accessed with methods `lower()` and `upper()`.
  73   */
  74
  75   std::ostringstream os;
  76   for (auto&& x : indexed(h, coverage::all)) {
  77     os << boost::format("bin %2i [%4.1f, %4.1f): %i\n")
  78           % x.index() % x.bin().lower() % x.bin().upper() % *x;
  79   }
  80
  81   std::cout << os.str() << std::flush;
  82
  83   assert(os.str() == "bin -1 [-inf, -1.0): 1\n"
  84                      "bin  0 [-1.0, -0.5): 1\n"
  85                      "bin  1 [-0.5, -0.0): 1\n"
  86                      "bin  2 [-0.0,  0.5): 2\n"
  87                      "bin  3 [ 0.5,  1.0): 0\n"
  88                      "bin  4 [ 1.0,  1.5): 1\n"
  89                      "bin  5 [ 1.5,  2.0): 1\n"
  90                      "bin  6 [ 2.0,  inf): 2\n");
  91 }
  92
  93 //]