Fixing category indexing (#298)

CHANGELOG.md

@@ -4,8 +4,10 @@ Documentation update. Now using development branch of Boost.Histogram again.
 
 #### Bug fixes
 
-* Allow slicing on flowless axes [#288][]
-* Sum repr fixed [#293][]
+* Fix sum over category axes in indexing [#298][]
+* Allow single category item selection [#298][]
+* Allow slicing on axes without flow bins [#288][]
+* Sum repr no longer throws error [#293][]
 
 #### Developer changes
 
@@ -14,6 +16,7 @@ Documentation update. Now using development branch of Boost.Histogram again.
 [#288]: https://github.com/scikit-hep/boost-histogram/pull/288
 [#292]: https://github.com/scikit-hep/boost-histogram/pull/292
 [#293]: https://github.com/scikit-hep/boost-histogram/pull/293
+[#298]: https://github.com/scikit-hep/boost-histogram/pull/298
 
 ### Version 0.6.1
 

boost_histogram/_internal/hist.py

@@ -484,6 +484,7 @@ def __getitem__(self, index):
         slices = []
         zeroes_start = []
         zeroes_stop = []
+        pick = dict()
 
         # We could use python's sum here, but for now, a private sum is used
         class ext_sum:
@@ -492,7 +493,8 @@ class ext_sum:
         # Compute needed slices and projections
         for i, ind in iterator:
             if hasattr(ind, "__index__"):
-                ind = slice(ind.__index__(), ind.__index__() + 1, ext_sum())
+                pick[i] = ind.__index__()
+                ind = slice(None)
 
             elif not isinstance(ind, slice):
                 raise IndexError(
@@ -508,6 +510,8 @@ class ext_sum:
                                 zeroes_start.append(i)
                             if ind.stop is not None:
                                 zeroes_stop.append(i)
+                            if ind.stop is None and ind.start is None:
+                                continue
                         elif hasattr(ind.step, "factor"):
                             merge = ind.step.factor
                         else:
@@ -530,11 +534,17 @@ class ext_sum:
                 slices.append(_core.algorithm.slice_and_rebin(i, begin, end, merge))
 
         reduced = self._reduce(*slices)
+
         if not integrations:
-            return self.__class__(reduced)
+            result = self.__class__(reduced)
         else:
             projections = [i for i in range(self.rank) if i not in integrations]
 
+            # For each axes projected out, we need to lower "pick" since it
+            # operates after the projection
+            reduce_ax = lambda ax: sum(i in projections for i in range(ax))
+            pick = {reduce_ax(ax): pick[ax] for ax in pick}
+
             # Replacement for crop missing in BH
             for i in zeroes_start:
                 if self.axes[i].options.underflow:
@@ -543,12 +553,34 @@ class ext_sum:
                 if self.axes[i].options.underflow:
                     reduced._hist._reset_row(i, reduced.axes[i].size)
 
-            return (
+            result = (
                 self.__class__(reduced.project(*projections))
                 if projections
                 else reduced.sum(flow=True)
             )
 
+        # Allow user to "pick" out values when mixed with slices
+        if pick:
+            # Sum out the axes. We will replace the contents, so "drop" would be
+            # just as good if there was one.
+            sresult = result[{ax: slice(None, None, ext_sum()) for ax in pick}]
+
+            # Make an array of selections, starting with [:,:,...,:]
+            bins_indexes = [slice(None)] * result.rank
+            # Now make the axis selections, remembering we will be in flow view
+            for ax in pick:
+                bins_indexes[ax] = pick[ax] + result._axis(ax).options.underflow
+
+            # If the result is a single value, we need to avoid [...]
+            if hasattr(sresult, "rank"):
+                sresult[...] = result.view(flow=True)[tuple(bins_indexes)]
+            else:
+                sresult = result.view(flow=True)[tuple(bins_indexes)]
+
+            result = sresult
+
+        return result
+
     def __setitem__(self, index, value):
         """
         There are several supported possibilities:

tests/test_histogram_indexing.py

@@ -218,3 +218,47 @@ def test_noflow_slicing():
 
     assert_array_equal(h[:, :, True].view(), vals)
     assert_array_equal(h[:, :, False].view(), 0)
+
+
+def test_pick_str_category():
+    noflow = dict(underflow=False, overflow=False)
+
+    h = bh.Histogram(
+        bh.axis.Regular(10, 0, 10),
+        bh.axis.Regular(10, 0, 10, **noflow),
+        bh.axis.StrCategory(["on", "off", "maybe"]),
+    )
+
+    vals = np.arange(100).reshape(10, 10)
+    h[:, :, bh.loc("on")] = vals
+
+    assert h[0, 1, bh.loc("on")] == 1
+    assert h[1, 0, bh.loc("on")] == 10
+    assert h[1, 1, bh.loc("on")] == 11
+    assert h[3, 4, bh.loc("maybe")] == 0
+
+    assert_array_equal(h[:, :, bh.loc("on")].view(), vals)
+    assert_array_equal(h[:, :, bh.loc("off")].view(), 0)
+
+
+def test_pick_int_category():
+    noflow = dict(underflow=False, overflow=False)
+
+    h = bh.Histogram(
+        bh.axis.Regular(10, 0, 10),
+        bh.axis.Regular(10, 0, 10, **noflow),
+        bh.axis.IntCategory([3, 5, 7]),
+    )
+
+    vals = np.arange(100).reshape(10, 10)
+    h[:, :, bh.loc(3)] = vals
+    h[:, :, bh.loc(5)] = vals + 1
+
+    assert h[0, 1, bh.loc(3)] == 1
+    assert h[1, 0, bh.loc(5)] == 10 + 1
+    assert h[1, 1, bh.loc(5)] == 11 + 1
+    assert h[3, 4, bh.loc(7)] == 0
+
+    assert_array_equal(h[:, :, bh.loc(3)].view(), vals)
+    assert_array_equal(h[:, :, bh.loc(5)].view(), vals + 1)
+    assert_array_equal(h[:, :, bh.loc(7)].view(), 0)