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

   1 // Copyright 2019 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_axis_basic_demo
   8
   9 #include <boost/histogram/axis.hpp>
  10 #include <limits>
  11
  12 int main() {
  13   using namespace boost::histogram;
  14
  15   // make a regular axis with 10 bins over interval from 1.5 to 2.5
  16   auto r = axis::regular<>{10, 1.5, 2.5};
  17   // `<>` is needed in C++14 because the axis is templated,
  18   // in C++17 you can do: auto r = axis::regular{10, 1.5, 2.5};
  19   assert(r.size() == 10);
  20   // alternatively, you can define the step size with the `step` marker
  21   auto r_step = axis::regular<>{axis::step(0.1), 1.5, 2.5};
  22   assert(r_step == r);
  23
  24   // histogram uses the `index` method to convert values to indices
  25   // note: intervals of builtin axis types are always semi-open [a, b)
  26   assert(r.index(1.5) == 0);
  27   assert(r.index(1.6) == 1);
  28   assert(r.index(2.4) == 9);
  29   // index for a value below the start of the axis is always -1
  30   assert(r.index(1.0) == -1);
  31   assert(r.index(-std::numeric_limits<double>::infinity()) == -1);
  32   // index for a value below the above the end of the axis is always `size()`
  33   assert(r.index(3.0) == 10);
  34   assert(r.index(std::numeric_limits<double>::infinity()) == 10);
  35   // index for not-a-number is also `size()` by convention
  36   assert(r.index(std::numeric_limits<double>::quiet_NaN()) == 10);
  37
  38   // make a variable axis with 3 bins [-1.5, 0.1), [0.1, 0.3), [0.3, 10)
  39   auto v = axis::variable<>{-1.5, 0.1, 0.3, 10.};
  40   assert(v.index(-2.0) == -1);
  41   assert(v.index(-1.5) == 0);
  42   assert(v.index(0.1) == 1);
  43   assert(v.index(0.3) == 2);
  44   assert(v.index(10) == 3);
  45   assert(v.index(20) == 3);
  46
  47   // make an integer axis with 3 bins at -1, 0, 1
  48   auto i = axis::integer<>{-1, 2};
  49   assert(i.index(-2) == -1);
  50   assert(i.index(-1) == 0);
  51   assert(i.index(0) == 1);
  52   assert(i.index(1) == 2);
  53   assert(i.index(2) == 3);
  54
  55   // make an integer axis called "foo"
  56   auto i_with_label = axis::integer<>{-1, 2, "foo"};
  57   // all builtin axis types allow you to pass some optional metadata as the last
  58   // argument in the constructor; a string by default, but can be any copyable type
  59
  60   // two axis do not compare equal if they differ in their metadata
  61   assert(i != i_with_label);
  62
  63   // integer axis also work well with unscoped enums
  64   enum { red, blue };
  65   auto i_for_enum = axis::integer<>{red, blue + 1};
  66   assert(i_for_enum.index(red) == 0);
  67   assert(i_for_enum.index(blue) == 1);
  68
  69   // make a category axis from a scoped enum and/or if the identifiers are not consecutive
  70   enum class Bar { red = 12, blue = 6 };
  71   auto c = axis::category<Bar>{Bar::red, Bar::blue};
  72   assert(c.index(Bar::red) == 0);
  73   assert(c.index(Bar::blue) == 1);
  74   // c.index(12) is a compile-time error, since the argument must be of type `Bar`
  75
  76   // category axis can be created for any copyable and equal-comparable type
  77   auto c_str = axis::category<std::string>{"red", "blue"};
  78   assert(c_str.index("red") == 0);
  79   assert(c_str.index("blue") == 1);
  80 }
  81
  82 //]