fix: allow axis + other

src/boost_histogram/tag.py

@@ -130,19 +130,19 @@ def __init__(
         edges: Sequence[int | float] | None = None,
         axis: PlottableAxis | None = None,
     ) -> None:
-        if (
-            sum(i is not None for i in [factor_or_axis, factor, groups, edges, axis])
-            != 1
-        ):
+        if isinstance(factor_or_axis, int):
+            factor = factor_or_axis
+        elif factor_or_axis is not None:
+            axis = factor_or_axis
+
+        total_args = sum(i is not None for i in [factor, groups, edges])
+        if total_args != 1 and axis is None:
             raise ValueError("Exactly one argument should be provided")
+
         self.groups = groups
         self.edges = edges
         self.axis = axis
         self.factor = factor
-        if isinstance(factor_or_axis, int):
-            self.factor = factor_or_axis
-        elif factor_or_axis is not None:
-            self.axis = factor_or_axis
 
     def __repr__(self) -> str:
         repr_str = f"{self.__class__.__name__}"
@@ -177,10 +177,10 @@ def group_mapping(self, axis: PlottableAxis) -> Sequence[int]:
             return [self.factor] * len(axis)
         if self.edges is not None or self.axis is not None:
             newedges = None
-            if self.axis is not None and hasattr(self.axis, "edges"):
-                newedges = self.axis.edges
-            elif self.edges is not None:
+            if self.edges is not None:
                 newedges = self.edges
+            elif self.axis is not None and hasattr(self.axis, "edges"):
+                newedges = self.axis.edges
 
             if newedges is not None and hasattr(axis, "edges"):
                 assert newedges[0] == axis.edges[0], "Edges must start at first bin"

tests/test_histogram.py

@@ -688,6 +688,24 @@
     assert_array_equal(hs.view(flow=True), [2, 2])
 
 
+def test_rebin_change_axis_int():
+    h = bh.Histogram(bh.axis.Regular(5, 0, 5))
+    h.fill([-1, 1.1, 2.2, 3.3, 4.4, 5.5])
+    hs = h[bh.rebin(edges=[0, 3, 5.0], axis=bh.axis.Integer(10, 12))]
+    assert_array_equal(hs.view(), [2, 2])
+    assert_array_equal(hs.view(flow=True), [1, 2, 2, 1])
+    assert_array_equal(hs.axes.edges[0], [10, 11, 12])
+
+
+def test_rebin_change_axis_cat():
+    h = bh.Histogram(bh.axis.Regular(5, 0, 5))
+    h.fill([-1, 1.1, 2.2, 3.3, 4.4, 5.5])
+    hs = h[bh.rebin(groups=[2, 2, 1], axis=bh.axis.StrCategory(["a", "b"]))]
+    assert_array_equal(hs.view(), [2, 2])
+    assert_array_equal(hs.view(flow=True), [1, 2, 2, 1])
+    assert_array_equal(hs.axes.edges[0], [10, 11, 12])
+
+
 def test_shrink_rebin_1d():
     h = bh.Histogram(bh.axis.Regular(20, 0, 4))
     h.fill(1.1)