added density method to indexed proxy, hide details of axes_buffer

include/boost/histogram/algorithm/project.hpp

@@ -39,7 +39,7 @@ auto project(const histogram<A, S>& h, mp11::mp_size_t<I> n, Ns... ns) {
           [&h](auto) { return S(unsafe_access::storage(h).get_allocator()); },
           [](auto) { return S(); }, 0));
 
-  detail::index_mapper im(h.rank());
+  detail::index_mapper<A> im(h.rank());
   auto iter = im.begin();
   std::size_t s = 1;
   h.for_each_axis([&](const auto& a) {
@@ -87,7 +87,7 @@ auto project(const histogram<A, S>& h, C c) {
       axes);
   r_axes.reserve(std::distance(begin, end));
 
-  detail::index_mapper im(h.rank());
+  detail::index_mapper<A> im(h.rank());
   auto iter = im.begin();
   std::size_t stride = 1;
   h.for_each_axis([&](const auto& a) {

include/boost/histogram/algorithm/reduce.hpp

@@ -8,7 +8,6 @@
 #define BOOST_HISTOGRAM_ALGORITHM_REDUCE_HPP
 
 #include <boost/assert.hpp>
-#include <boost/container/static_vector.hpp>
 #include <boost/histogram/detail/axes.hpp>
 #include <boost/histogram/detail/index_mapper.hpp>
 #include <boost/histogram/detail/meta.hpp>
@@ -66,8 +65,7 @@ reduce_option_type rebin(unsigned merge) { return rebin(0, merge); }
 
 template <typename A, typename S, typename C, typename = detail::requires_iterable<C>>
 histogram<A, S> reduce(const histogram<A, S>& h, const C& c) {
-  auto options =
-      boost::container::static_vector<reduce_option_type, axis::limit>(h.rank());
+  auto options = detail::axes_buffer<A, reduce_option_type>(h.rank());
   for (const auto& o : c) {
     auto& opt_ref = options[o.iaxis];
     if (opt_ref) throw std::invalid_argument("indices must be unique");
@@ -78,7 +76,7 @@ histogram<A, S> reduce(const histogram<A, S>& h, const C& c) {
 
   auto r_axes = detail::make_empty_axes(unsafe_access::axes(h));
 
-  detail::index_mapper_reduce im(h.rank());
+  detail::index_mapper_reduce<A> im(h.rank());
   auto im_iter = im.begin();
   std::size_t stride[2] = {1, 1};
   unsigned iaxis = 0;

include/boost/histogram/axis/traits.hpp

@@ -61,6 +61,19 @@ unsigned extend(const T& t) noexcept {
   return t.size() + (opt & option_type::underflow) + (opt & option_type::overflow);
 }
 
+template <typename T>
+double width(const T& t, unsigned idx) {
+  return detail::static_if<detail::has_method_value<detail::unqual<T>, double>>(
+      [&](const auto& a) {
+        using Arg = detail::unqual<detail::arg_type<detail::unqual<decltype(a)>>>;
+        return detail::static_if<std::is_integral<Arg>>(
+            [&](const auto&) -> double { return 1; },
+            [&](const auto& a) -> double { return a.value(idx + 1) - a.value(idx); }, a);
+      },
+      [](const auto&) -> double { throw std::runtime_error("axis has no value method"); },
+      t);
+}
+
 } // namespace traits
 } // namespace axis
 } // namespace histogram

include/boost/histogram/detail/axes.hpp

@@ -20,6 +20,18 @@
 #include <type_traits>
 #include <vector>
 
+/* Most of the histogram code is generic and works for any number of axes. Buffers with a
+ * fixed maximum capacity are used in some places, which have a size equal to the rank of
+ * a histogram. The buffers are statically allocated to improve performance, which means
+ * that they need a preset maximum capacity. 32 seems like a safe upper limit for the rank
+ * (you can nevertheless increase it here if necessary): the simplest non-trivial axis has
+ * 2 bins; even if counters are used which need only a byte of storage per bin, this still
+ * corresponds to 4 GB of storage.
+ */
+#ifndef BOOST_HISTOGRAM_DETAIL_AXES_LIMIT
+#define BOOST_HISTOGRAM_DETAIL_AXES_LIMIT 32
+#endif
+
 namespace boost {
 namespace histogram {
 namespace detail {
@@ -151,10 +163,11 @@ void for_each_axis(const T& axes, F&& f) {
   for (const auto& x : axes) { axis::visit(std::forward<F>(f), x); }
 }
 
-template <typename T, typename A>
-using make_axes_buffer = boost::container::static_vector<
-    T, mp11::mp_eval_if_c<!(has_fixed_size<A>::value), mp11::mp_size_t<axis::limit>,
-                          std::tuple_size, A>::value>;
+template <typename Axes, typename T>
+using axes_buffer = boost::container::static_vector<
+    T, mp11::mp_eval_if_c<!(has_fixed_size<Axes>::value),
+                          mp11::mp_size_t<BOOST_HISTOGRAM_DETAIL_AXES_LIMIT>,
+                          std::tuple_size, Axes>::value>;
 
 template <typename T>
 auto make_empty_axes(const T& t) {

include/boost/histogram/detail/index_mapper.hpp

@@ -16,16 +16,14 @@ namespace boost {
 namespace histogram {
 namespace detail {
 
-struct index_mapper_item {
-  std::size_t stride[2];
-};
+template <typename A>
+struct index_mapper {
+  struct item {
+    std::size_t stride[2];
+  };
+  using buffer_type = axes_buffer<A, item>;
 
-class index_mapper
-    : public boost::container::static_vector<index_mapper_item, axis::limit> {
-public:
-  std::size_t total = 1;
-
-  index_mapper(unsigned dim) : static_vector(dim) {}
+  index_mapper(unsigned dim) : buffer(dim) {}
 
   template <typename T, typename U>
   void operator()(T& dst, const U& src) {
@@ -42,19 +40,26 @@ public:
       dst.add(j, src[i]);
     }
   }
-};
 
-struct index_mapper_reduce_item {
-  std::size_t stride[2];
-  int underflow[2], overflow[2], begin, end, merge;
-};
+  decltype(auto) begin() { return buffer.begin(); }
+  decltype(auto) end() { return buffer.end(); }
 
-class index_mapper_reduce
-    : public boost::container::static_vector<index_mapper_reduce_item, axis::limit> {
-public:
+  decltype(auto) operator[](unsigned i) { return buffer[i]; }
+
+  buffer_type buffer;
   std::size_t total = 1;
+};
 
-  index_mapper_reduce(unsigned dim) : static_vector(dim) {}
+template <typename A>
+class index_mapper_reduce {
+public:
+  struct item {
+    std::size_t stride[2];
+    int underflow[2], overflow[2], begin, end, merge;
+  };
+  using buffer_type = axes_buffer<A, item>;
+
+  index_mapper_reduce(unsigned dim) : buffer(dim) {}
 
   template <typename T, typename U>
   void operator()(T& dst, const U& src) {
@@ -80,6 +85,14 @@ public:
       if (!drop) dst.add(j, src[i]);
     }
   }
+
+  decltype(auto) begin() { return buffer.begin(); }
+  decltype(auto) end() { return buffer.end(); }
+
+  decltype(auto) operator[](unsigned i) { return buffer[i]; }
+
+  buffer_type buffer;
+  std::size_t total = 1;
 };
 } // namespace detail
 } // namespace histogram

include/boost/histogram/detail/is_set.hpp

@@ -10,7 +10,6 @@
 #include <boost/container/flat_set.hpp>
 #include <boost/container/static_vector.hpp>
 #include <boost/histogram/detail/meta.hpp>
-#include <boost/histogram/histogram_fwd.hpp> // for axis::limit
 
 namespace boost {
 namespace histogram {
@@ -18,7 +17,7 @@ namespace detail {
 template <class Iterator>
 bool is_set(Iterator begin, Iterator end) {
   using T = iterator_value_type<Iterator>;
-  using C = boost::container::static_vector<T, axis::limit>;
+  using C = boost::container::static_vector<T, BOOST_HISTOGRAM_DETAIL_AXES_LIMIT>;
   boost::container::flat_set<T, std::less<T>, C> s(begin, end);
   return static_cast<std::size_t>(std::distance(begin, end)) == s.size();
 }

include/boost/histogram/histogram.hpp

@@ -30,8 +30,9 @@ public:
   using axes_type = Axes;
   using storage_type = Storage;
   using value_type = typename storage_type::value_type;
-  using iterator = typename storage_type::const_iterator; // for boost::range_iterator
-  using const_iterator = typename storage_type::const_iterator;
+  // typedefs for boost::range_iterator
+  using iterator = decltype(std::declval<storage_type&>().begin());
+  using const_iterator = decltype(std::declval<const storage_type&>().begin());
 
   histogram() = default;
   histogram(const histogram& rhs) = default;

include/boost/histogram/histogram_fwd.hpp

@@ -18,21 +18,6 @@ namespace boost {
 namespace histogram {
 namespace axis {
 
-/* Most of the histogram code is generic and works for any number of axes. Buffers with a
- * fixed maximum capacity are used in some places, which have a size equal to the rank of
- * a histogram. The buffers are statically allocated to improve performance, which means
- * that they need a preset maximum capacity. 32 seems like a safe upper limit for the rank
- * (you can nevertheless increase it here if necessary): the simplest non-trivial axis has
- * 2 bins; even if counters are used which need only a byte of storage per bin, this still
- * corresponds to 4 GB of storage.
- */
-BOOST_ATTRIBUTE_UNUSED static constexpr unsigned limit =
-#ifdef BOOST_HISTOGRAM_AXES_LIMIT
-    BOOST_HISTOGRAM_AXES_LIMIT;
-#else
-    32;
-#endif
-
 /// empty metadata type
 struct null_type {};
 

include/boost/histogram/indexed.hpp

@@ -7,13 +7,13 @@
 #ifndef BOOST_HISTOGRAM_INDEXED_HPP
 #define BOOST_HISTOGRAM_INDEXED_HPP
 
-#include <boost/container/static_vector.hpp>
 #include <boost/histogram/axis/traits.hpp>
 #include <boost/histogram/detail/axes.hpp>
 #include <boost/histogram/detail/meta.hpp>
 #include <boost/histogram/histogram_fwd.hpp>
 #include <boost/histogram/unsafe_access.hpp>
 #include <boost/iterator/iterator_facade.hpp>
+#include <boost/mp11.hpp>
 #include <utility>
 
 namespace boost {
@@ -29,8 +29,8 @@ class indexed_range {
     std::size_t stride;
     int underflow;
   };
-  using strides_type = detail::make_axes_buffer<stride_t, axes_type>;
-  using index_type = detail::make_axes_buffer<int, axes_type>;
+  using strides_type = detail::axes_buffer<axes_type, stride_t>;
+  using index_type = detail::axes_buffer<axes_type, int>;
   using value_type = decltype(std::declval<storage_type&>()[0]);
 
 public:
@@ -42,11 +42,20 @@ public:
     decltype(auto) bin(mp11::mp_size_t<N>) const {
       return detail::axis_get<N>(axes_)[(*this)[N]];
     }
+
     decltype(auto) bin(unsigned d) const {
       return detail::axis_get(axes_, d)[(*this)[d]];
     }
 
-    value_type value;
+    double density() const {
+      double x = 1;
+      auto it = this->begin();
+      detail::for_each_axis(axes_,
+                            [&](const auto& a) { x *= axis::traits::width(a, *it++); });
+      return value / x;
+    }
+
+    const value_type value;
 
   protected:
     index_value(const axes_type& a, value_type v)

test/indexed_test.cpp

@@ -7,6 +7,7 @@
 #include <boost/core/lightweight_test.hpp>
 #include <boost/histogram/axis/integer.hpp>
 #include <boost/histogram/axis/ostream_operators.hpp>
+#include <boost/histogram/axis/variable.hpp>
 #include <boost/histogram/histogram.hpp>
 #include <boost/histogram/indexed.hpp>
 #include <boost/histogram/literals.hpp>
@@ -105,6 +106,22 @@ void run_tests() {
     ++it;
     BOOST_TEST(it == ind.end());
   }
+
+  {
+    auto ax = axis::variable<>({0.0, 0.1, 0.3, 0.6});
+    auto ay = axis::integer<int>(0, 2);
+    auto az = ax;
+    auto h = make_s(Tag(), std::vector<int>(), ax, ay, az);
+
+    // fill uniformly
+    for (auto x : indexed(h)) {
+      h(x.bin(0).center(), x.bin(1).value(), x.bin(2).center());
+    }
+
+    for (auto x : indexed(h)) {
+      BOOST_TEST_EQ(x.density(), x.value / (x.bin(0).width() * x.bin(2).width()));
+    }
+  }
 }
 
 int main() {