[hist] Implement RHistEngine::SetBinContent

This needs one indirection to construct the std::array of indices
with the right (number of) elements.

Author: hahnjo

hist/histv7/doc/DesignImplementation.md

@@ -58,11 +58,12 @@ Special arguments are passed last.
 Examples include
 ```cpp
 template <typename... A> void Fill(const std::tuple<A...> &args, RWeight w);
-template <std::size_t N> void SetBinContent(const std::array<RBinIndex, N> &indices, const BinContentType &content);
+template <std::size_t N, typename V> void SetBinContent(const std::array<RBinIndex, N> &indices, const V &value);
 ```
-The same works for the variadic function templates that will check the type of the last argument.
+Note that we accept mandatory arguments with a template type as well to allow automatic conversion.
 
-For profiles, we accept the value with a template type as well to allow automatic conversion to `double`, for example from `int`.
+Variadic function templates receive all arguments in a single function parameter pack.
+For optional arguments, the function will check the type of the last argument to determine if it was passed.
 
 ## Miscellaneous
 

hist/histv7/inc/ROOT/RHistEngine.hxx

@@ -170,6 +170,78 @@ public:
       return GetBinContent(indices);
    }
 
+   /// Set the content of a single bin.
+   ///
+   /// \code
+   /// ROOT::Experimental::RHistEngine<int> hist({/* two dimensions */});
+   /// std::array<ROOT::Experimental::RBinIndex, 2> indices = {3, 5};
+   /// int value = /* ... */;
+   /// hist.SetBinContent(indices, value);
+   /// \endcode
+   ///
+   /// \note Compared to TH1 conventions, the first normal bin has index 0 and underflow and overflow bins are special
+   /// values. See also the class documentation of RBinIndex.
+   ///
+   /// Throws an exception if the number of indices does not match the axis configuration or the bin is not found.
+   ///
+   /// \param[in] indices the array of indices for each axis
+   /// \param[in] value the new value of the bin content
+   /// \par See also
+   /// the \ref SetBinContent(const A &... args) const "variadic function template overload" accepting arguments
+   /// directly
+   template <std::size_t N, typename V>
+   void SetBinContent(const std::array<RBinIndex, N> &indices, const V &value)
+   {
+      // We could rely on RAxes::ComputeGlobalIndex to check the number of arguments, but its exception message might
+      // be confusing for users.
+      if (N != GetNDimensions()) {
+         throw std::invalid_argument("invalid number of indices passed to SetBinContent");
+      }
+      RLinearizedIndex index = fAxes.ComputeGlobalIndex(indices);
+      if (!index.fValid) {
+         throw std::invalid_argument("bin not found in SetBinContent");
+      }
+      assert(index.fIndex < fBinContents.size());
+      // To allow conversion, we have to accept value with a template type V to capture any argument. Otherwise it would
+      // select the variadic function template...
+      fBinContents[index.fIndex] = value;
+   }
+
+private:
+   template <typename... A, std::size_t... I>
+   void SetBinContentImpl(const std::tuple<A...> &args, std::index_sequence<I...>)
+   {
+      std::array<RBinIndex, sizeof...(A) - 1> indices{std::get<I>(args)...};
+      SetBinContent(indices, std::get<sizeof...(A) - 1>(args));
+   }
+
+public:
+   /// Set the content of a single bin.
+   ///
+   /// \code
+   /// ROOT::Experimental::RHistEngine<int> hist({/* two dimensions */});
+   /// int value = /* ... */;
+   /// hist.SetBinContent(ROOT::Experimental::RBinIndex(3), ROOT::Experimental::RBinIndex(5), value);
+   /// // ... or construct the RBinIndex arguments implicitly from integers:
+   /// hist.SetBinContent(3, 5, value);
+   /// \endcode
+   ///
+   /// \note Compared to TH1 conventions, the first normal bin has index 0 and underflow and overflow bins are special
+   /// values. See also the class documentation of RBinIndex.
+   ///
+   /// Throws an exception if the number of arguments does not match the axis configuration or the bin is not found.
+   ///
+   /// \param[in] args the arguments for each axis and the new value of the bin content
+   /// \par See also
+   /// the \ref SetBinContent(const std::array<RBinIndex, N> &indices, const V &value) const "function overload"
+   /// accepting `std::array`
+   template <typename... A>
+   void SetBinContent(const A &...args)
+   {
+      auto t = std::forward_as_tuple(args...);
+      SetBinContentImpl(t, std::make_index_sequence<sizeof...(A) - 1>());
+   }
+
    /// Add all bin contents of another histogram.
    ///
    /// Throws an exception if the axes configurations are not identical.

hist/histv7/test/hist_engine.cxx

@@ -71,6 +71,55 @@ TEST(RHistEngine, GetBinContentNotFound)
    EXPECT_THROW(engine.GetBinContent(Bins), std::invalid_argument);
 }
 
+TEST(RHistEngine, SetBinContent)
+{
+   static constexpr std::size_t Bins = 20;
+   const RRegularAxis axis(Bins, {0, Bins});
+   RHistEngine<int> engine({axis});
+
+   const RBinIndex index(7);
+   engine.SetBinContent(index, 42);
+   EXPECT_EQ(engine.GetBinContent(index), 42);
+
+   const std::array<RBinIndex, 1> indices = {index};
+   engine.SetBinContent(indices, 43);
+   EXPECT_EQ(engine.GetBinContent(indices), 43);
+
+   // This also works if the value must be converted to the bin content type.
+   RHistEngine<float> engineF({axis});
+   engineF.SetBinContent(index, 42);
+   EXPECT_EQ(engineF.GetBinContent(index), 42);
+
+   engineF.SetBinContent(indices, 43);
+   EXPECT_EQ(engineF.GetBinContent(indices), 43);
+}
+
+TEST(RHistEngine, SetBinContentInvalidNumberOfArguments)
+{
+   static constexpr std::size_t Bins = 20;
+   const RRegularAxis axis(Bins, {0, Bins});
+   RHistEngine<int> engine1({axis});
+   ASSERT_EQ(engine1.GetNDimensions(), 1);
+   RHistEngine<int> engine2({axis, axis});
+   ASSERT_EQ(engine2.GetNDimensions(), 2);
+
+   EXPECT_NO_THROW(engine1.SetBinContent(1, 0));
+   EXPECT_THROW(engine1.SetBinContent(1, 2, 0), std::invalid_argument);
+
+   EXPECT_THROW(engine2.SetBinContent(1, 0), std::invalid_argument);
+   EXPECT_NO_THROW(engine2.SetBinContent(1, 2, 0));
+   EXPECT_THROW(engine2.SetBinContent(1, 2, 3, 0), std::invalid_argument);
+}
+
+TEST(RHistEngine, SetBinContentNotFound)
+{
+   static constexpr std::size_t Bins = 20;
+   const RRegularAxis axis(Bins, {0, Bins});
+   RHistEngine<int> engine({axis});
+
+   EXPECT_THROW(engine.SetBinContent(Bins, 0), std::invalid_argument);
+}
+
 TEST(RHistEngine, Add)
 {
    static constexpr std::size_t Bins = 20;

hist/histv7/test/hist_user.cxx

@@ -6,6 +6,12 @@
 struct User {
    double fValue = 0;
 
+   User &operator=(double value)
+   {
+      fValue = value;
+      return *this;
+   }
+
    User &operator++()
    {
       fValue++;
@@ -119,3 +125,19 @@ TEST(RHistEngineUser, FillWeight)
    std::array<RBinIndex, 1> indices = {9};
    EXPECT_EQ(engine.GetBinContent(indices).fValue, 0.9);
 }
+
+TEST(RHistEngineUser, SetBinContent)
+{
+   // Setting uses operator=
+   static constexpr std::size_t Bins = 20;
+   const RRegularAxis axis(Bins, {0, Bins});
+   RHistEngine<User> engine({axis});
+
+   const RBinIndex index(7);
+   engine.SetBinContent(index, 42);
+   EXPECT_EQ(engine.GetBinContent(index).fValue, 42);
+
+   const std::array<RBinIndex, 1> indices = {index};
+   engine.SetBinContent(indices, 43);
+   EXPECT_EQ(engine.GetBinContent(indices).fValue, 43);
+}