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NCAS-CMS · Jul 16, 2024 · f3ad202 · f3ad202
1 parent f8c7575
commit f3ad202
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Showing 2 changed files with 15 additions and 86 deletions.
diff --git a/cf/maths.py b/cf/maths.py
@@ -308,7 +308,8 @@ def histogram(*digitized, density=False):
 
     if density:
         # Get the measure of each bin. This is the outer product of
-        # the cell sizes of each dimension coordinate construct.
+        # the cell sizes of each dimension coordinate construct (the
+        # dimension coordinate constructs define the bins).
         data_axes = out.get_data_axes()
         dim = out.dimension_coordinate(filter_by_axis=(data_axes[0],))
         bin_measures = dim.cellsize

diff --git a/cf/test/test_Maths.py b/cf/test/test_Maths.py
@@ -216,35 +216,23 @@ def test_histogram(self):
         g[...] = np.arange(40).reshape(5, 8) + 253.15
         g.override_units("K", inplace=True)
 
+        atol = 1e-15
+
         # 1-d histogram
         indices = f.digitize(10)
         h = cf.histogram(indices)
         self.assertTrue((h.array == [9, 7, 9, 4, 5, 1, 1, 1, 2, 1]).all)
         h = cf.histogram(indices, density=True)
-        self.assertTrue(
-            (
-                h.array
-                == [
-                    15.734265734265733,
-                    12.237762237762242,
-                    15.734265734265733,
-                    6.9930069930069925,
-                    8.74125874125874,
-                    1.748251748251749,
-                    1.7482517482517475,
-                    1.748251748251749,
-                    3.496503496503498,
-                    1.748251748251744,
-                ]
-            ).all
-        )
-        integral = (h * h.dimension_coordinate().cellsize).sum()
-        self.assertEqual(integral.array, 1)
+        # Check that integral is 1
+        bin_measures = h.dimension_coordinate().cellsize
+        integral = (h * bin_measures).sum()
+        self.assertTrue(np.allclose(integral.array, 1, rtol=0, atol=atol))
 
         # 2-d histogram
         indices_t = g.digitize(5)
         h = cf.histogram(indices, indices_t)
         self.assertEqual(h.Units, cf.Units())
+        # The -1 values correspond to missing values in h
         self.assertTrue(
             (
                 h.array
@@ -260,73 +248,13 @@ def test_histogram(self):
 
         h = cf.histogram(indices, indices_t, density=True)
         self.assertEqual(h.Units, cf.Units())
-        self.assertTrue(
-            (
-                h.array
-                == [
-                    [
-                        0.6724045185583661,
-                        0.6724045185583664,
-                        0.44826967903891074,
-                        -1,
-                        -1,
-                        -1,
-                        -1,
-                        -1,
-                        -1,
-                        -1,
-                    ],
-                    [
-                        0.22413483951945457,
-                        0.2241348395194546,
-                        0.44826967903890913,
-                        0.22413483951945457,
-                        0.6724045185583637,
-                        -1,
-                        -1,
-                        -1,
-                        -1,
-                        -1,
-                    ],
-                    [
-                        0.22413483951945457,
-                        -1,
-                        -1,
-                        0.22413483951945457,
-                        -1,
-                        0.2241348395194547,
-                        0.22413483951945448,
-                        0.2241348395194547,
-                        0.4482696790389094,
-                        0.224134839519454,
-                    ],
-                    [
-                        0.4482696790389124,
-                        0.22413483951945626,
-                        0.2241348395194562,
-                        0.4482696790389124,
-                        0.4482696790389124,
-                        -1,
-                        -1,
-                        -1,
-                        -1,
-                        -1,
-                    ],
-                    [
-                        0.4482696790389059,
-                        0.44826967903890597,
-                        0.8965393580778118,
-                        -1,
-                        -1,
-                        -1,
-                        -1,
-                        -1,
-                        -1,
-                        -1,
-                    ],
-                ]
-            ).all()
+        # Check that integral is 1
+        bin_measures = h.dimension_coordinate("air_temperature").cellsize
+        bin_measures.outerproduct(
+            h.dimension_coordinate("specific_humidity").cellsize, inplace=True
         )
+        integral = (h * bin_measures).sum()
+        self.assertTrue(np.allclose(integral.array, 1, rtol=0, atol=atol))
 
 
 if __name__ == "__main__":