adds Add operator to FEMap

cinnabar/femap.py

@@ -72,6 +72,8 @@ def read_csv(filepath: pathlib.Path, units: Optional[openff.units.Quantity] = No
 class FEMap:
     """Free Energy map of both simulations and bench measurements
 
+    Contains a set (non-duplicate entries) of different measurements.
+
     Examples
     --------
     To read from a csv file specifically formatted for this, you can use:
@@ -120,6 +122,22 @@ def __eq__(self, other):
         # iter returns hashable Measurements, so this will compare contents
         return set(self) == set(other)
 
+    def __add__(self, other):
+        if not isinstance(other, self.__class__):
+            return NotImplemented
+        # deduplicate based on hashing the Measurements from iter
+        my_items = set(self)
+        other_items = set(other)
+
+        new = self.__class__()
+        for m in my_items | other_items:
+            new.add_measurement(m)
+
+        return new
+
+    def __len__(self):
+        return len(list(iter(self)))
+
     def to_networkx(self) -> nx.MultiDiGraph:
         """A *copy* of the FEMap as a networkx Graph
 

cinnabar/tests/test_femap.py

@@ -225,3 +225,71 @@ def test_from_networkx(example_map):
     m2 = cinnabar.FEMap.from_networkx(g)
 
     assert example_map == m2
+
+
+def test_add():
+    m1 = cinnabar.FEMap()
+    m1.add_experimental_measurement(
+        label='c1',
+        value=10.1 * unit.nanomolar,
+        uncertainty=0.2 * unit.nanomolar,
+    )
+    m1.add_experimental_measurement(
+        label='c2',
+        value=10.2 * unit.nanomolar,
+        uncertainty=0.3 * unit.nanomolar,
+    )
+
+    m2 = cinnabar.FEMap()
+    m2.add_absolute_calculation(
+        label='c1',
+        value=-9.5 * unit.kilocalorie_per_mole,
+        uncertainty=0.4 * unit.kilocalorie_per_mole,
+    )
+
+    m3 = m1 + m2
+
+    assert len(m3) == 3
+    measurements = set(m3)
+
+    ref1 = set(m1)
+    ref2 = set(m2)
+
+    assert measurements == ref1 | ref2
+
+
+def test_add_duplicate():
+    # adding, but the two maps have a duplicate measurement
+    m1 = cinnabar.FEMap()
+    m1.add_experimental_measurement(
+        label='c1',
+        value=10.1 * unit.nanomolar,
+        uncertainty=0.2 * unit.nanomolar,
+    )
+    m1.add_experimental_measurement(
+        label='c2',
+        value=10.2 * unit.nanomolar,
+        uncertainty=0.3 * unit.nanomolar,
+    )
+
+    m2 = cinnabar.FEMap()
+    m2.add_experimental_measurement(
+        label='c1',
+        value=10.1 * unit.nanomolar,
+        uncertainty=0.2 * unit.nanomolar,
+    )
+    m2.add_absolute_calculation(
+        label='c1',
+        value=-9.5 * unit.kilocalorie_per_mole,
+        uncertainty=0.4 * unit.kilocalorie_per_mole,
+    )
+
+    m3 = m1 + m2
+
+    assert len(m3) == 3
+    measurements = set(m3)
+
+    ref1 = set(m1)
+    ref2 = set(m2)
+
+    assert measurements == ref1 | ref2