[Python][UHI] Fix handling of infinite upper bin edges in sliced histograms

bindings/pyroot/pythonizations/test/uhi_indexing.py

@@ -2,6 +2,7 @@
 Tests to verify that TH1 and derived histograms conform to the UHI Indexing interfaces (setting, accessing and slicing).
 """
 
+import numpy as np
 import pytest
 import ROOT
 from ROOT._pythonization._uhi import _get_axis, _get_processed_slices, _overflow, _shape, _underflow
@@ -326,5 +327,35 @@ def test_list_iter(self, hist_setup):
         assert list(hist_setup) == expected.flatten().tolist()
 
 
+class TestInfiniteEdges:
+    def setup_method(self):
+        # create a 2D histogram with an infinite upper edge on the Y axis
+        xedges = np.array([0.0, 1.0, 2.0], dtype="float64")
+        yedges = np.array([0.0, 1.0, 2.0, np.inf], dtype="float64")
+        self.h_inf = ROOT.TH2D("h_inf", "h_inf", len(xedges) - 1, xedges, len(yedges) - 1, yedges)
+
+        for i in range(1, self.h_inf.GetNbinsX() + 1):
+            for j in range(1, self.h_inf.GetNbinsY() + 1):
+                self.h_inf.SetBinContent(i, j, 10 * i + j)
+
+    def test_uhi_projection_preserves_content(self):
+        """check that UHI projection behaves like standard projection"""
+        # projection on X axis
+        proj_x_ref = self.h_inf.ProjectionX()
+        proj_x_uhi = self.h_inf[:, ROOT.uhi.sum]
+        ref_values = proj_x_ref.values()
+        uhi_values = proj_x_uhi.values()
+
+        assert np.allclose(uhi_values, ref_values)
+
+        # projection on Y axis
+        proj_y_ref = self.h_inf.ProjectionY()
+        proj_y_uhi = self.h_inf[ROOT.uhi.sum, :]
+        ref_values = proj_y_ref.values()
+        uhi_values = proj_y_uhi.values()
+
+        assert np.allclose(uhi_values, ref_values)
+
+
 if __name__ == "__main__":
     raise SystemExit(pytest.main(args=[__file__]))

hist/hist/inc/TH1.h

@@ -214,17 +214,19 @@ class TH1 : public TNamed, public TAttLine, public TAttFill, public TAttMarker {
 
       // Compute new bin counts and edges
       std::array<Int_t, kMaxDim> nBins{}, totalBins{};
-      std::array<Double_t, kMaxDim> lowEdge{}, upEdge{};
+      std::array<std::vector<Double_t>, kMaxDim> edges;
       for (decltype(ndim) d = 0; d < ndim; ++d) {
          const auto &axis = (d == 0 ? fXaxis : d == 1 ? fYaxis : fZaxis);
          auto start = std::max(1, args[d * 2]);
          auto end = std::min(axis.GetNbins() + 1, args[d * 2 + 1]);
          nBins[d] = end - start;
-         lowEdge[d] = axis.GetBinLowEdge(start);
-         upEdge[d] = axis.GetBinLowEdge(end);
          totalBins[d] = axis.GetNbins() + 2;
          args[2 * d] = start;
          args[2 * d + 1] = end;
+         // Compute new edges
+         for (int b = start; b <= end; ++b)
+            edges[d].push_back(axis.GetBinLowEdge(b));
+         edges[d].push_back(axis.GetBinUpEdge(end));
       }
 
       // Compute layout sizes for slice
@@ -271,13 +273,10 @@ class TH1 : public TNamed, public TAttLine, public TAttFill, public TAttMarker {
       dataArray = newArr;
 
       // Reconfigure Axes
-      if (ndim == 1) {
-         this->SetBins(nBins[0], lowEdge[0], upEdge[0]);
-      } else if (ndim == 2) {
-         this->SetBins(nBins[0], lowEdge[0], upEdge[0], nBins[1], lowEdge[1], upEdge[1]);
-      } else if (ndim == 3) {
-         this->SetBins(nBins[0], lowEdge[0], upEdge[0], nBins[1], lowEdge[1], upEdge[1], nBins[2], lowEdge[2],
-                       upEdge[2]);
+      switch (ndim) {
+      case 1: this->SetBins(nBins[0], edges[0].data()); break;
+      case 2: this->SetBins(nBins[0], edges[0].data(), nBins[1], edges[1].data()); break;
+      case 3: this->SetBins(nBins[0], edges[0].data(), nBins[1], edges[1].data(), nBins[2], edges[2].data()); break;
       }
 
       // Update the statistics