[hist] Enable RHist with RCategoricalAxis

Author: hahnjo

hist/histv7/inc/ROOT/RHist.hxx

@@ -6,6 +6,7 @@
 #define ROOT_RHist
 
 #include "RBinIndex.hxx"
+#include "RCategoricalAxis.hxx"
 #include "RHistEngine.hxx"
 #include "RHistStats.hxx"
 #include "RWeight.hxx"
@@ -17,6 +18,7 @@
 #include <stdexcept>
 #include <tuple>
 #include <utility>
+#include <variant>
 #include <vector>
 
 class TBuffer;
@@ -73,7 +75,16 @@ public:
    /// Construct a histogram.
    ///
    /// \param[in] axes the axis objects, must have size > 0
-   explicit RHist(std::vector<RAxisVariant> axes) : fEngine(std::move(axes)), fStats(fEngine.GetNDimensions()) {}
+   explicit RHist(std::vector<RAxisVariant> axes) : fEngine(std::move(axes)), fStats(fEngine.GetNDimensions())
+   {
+      // The axes parameter was moved, use from the engine.
+      const auto &engineAxes = fEngine.GetAxes();
+      for (std::size_t i = 0; i < engineAxes.size(); i++) {
+         if (std::get_if<RCategoricalAxis>(&engineAxes[i])) {
+            fStats.DisableDimension(i);
+         }
+      }
+   }
 
    /// Construct a one-dimensional histogram engine with a regular axis.
    ///

hist/histv7/test/hist_hist.cxx

@@ -172,6 +172,43 @@ TEST(RHist, FillWeight)
    EXPECT_FLOAT_EQ(hist.ComputeStdDev(), 0.49913420);
 }
 
+TEST(RHist, FillCategorical)
+{
+   const std::vector<std::string> categories = {"a", "b", "c"};
+   const RCategoricalAxis axis(categories);
+   RHist<int> hist({axis});
+
+   hist.Fill("b");
+   hist.Fill(std::make_tuple("c"));
+
+   EXPECT_EQ(hist.GetBinContent(RBinIndex(1)), 1);
+   std::array<RBinIndex, 1> indices = {2};
+   EXPECT_EQ(hist.GetBinContent(indices), 1);
+
+   EXPECT_EQ(hist.GetNEntries(), 2);
+   EXPECT_FLOAT_EQ(hist.ComputeNEffectiveEntries(), 2);
+}
+
+TEST(RHist, FillCategoricalWeight)
+{
+   const std::vector<std::string> categories = {"a", "b", "c"};
+   const RCategoricalAxis axis(categories);
+   RHist<float> hist({axis});
+
+   hist.Fill("b", RWeight(0.8));
+   hist.Fill(std::make_tuple("c"), RWeight(0.9));
+
+   EXPECT_FLOAT_EQ(hist.GetBinContent(RBinIndex(1)), 0.8);
+   std::array<RBinIndex, 1> indices = {2};
+   EXPECT_FLOAT_EQ(hist.GetBinContent(indices), 0.9);
+
+   EXPECT_EQ(hist.GetNEntries(), 2);
+   EXPECT_FLOAT_EQ(hist.GetStats().GetSumW(), 1.7);
+   EXPECT_FLOAT_EQ(hist.GetStats().GetSumW2(), 1.45);
+   // Cross-checked with TH1
+   EXPECT_FLOAT_EQ(hist.ComputeNEffectiveEntries(), 1.9931034);
+}
+
 TEST(RHist, Scale)
 {
    static constexpr std::size_t Bins = 20;