Add HazardForecast.concat (#1184)

* Add HazardForecast.concat

Author: peanutfun

climada/hazard/forecast.py

@@ -105,6 +105,16 @@ def _check_sizes(self):
         size(exp_len=num_entries, var=self.member, var_name="Forecast.member")
         size(exp_len=num_entries, var=self.lead_time, var_name="Forecast.lead_time")
 
+    @classmethod
+    def concat(cls, haz_list: list):
+        """Concatenate multiple HazardForecast instances and return a new object"""
+        if len(haz_list) == 0:
+            return cls()
+        hazard = Hazard.concat(haz_list)
+        lead_time = np.concatenate(tuple(haz.lead_time for haz in haz_list))
+        member = np.concatenate(tuple(haz.member for haz in haz_list))
+        return cls.from_hazard(hazard, lead_time=lead_time, member=member)
+
     def select(
         self,
         member=None,

climada/hazard/test/test_forecast.py

@@ -95,16 +95,37 @@ def test_from_hazard(lead_time, member, hazard, haz_kwargs):
     assert_hazard_kwargs(haz_fc_from_haz, **haz_kwargs)
 
 
-@pytest.mark.skip("Concat from base class does not work")
-def test_hazard_forecast_concat(haz_fc, lead_time, member):
-    haz_fc1 = haz_fc.select(event_id=[1, 2])
-    haz_fc2 = haz_fc.select(event_id=[3, 4])
-    haz_fc_concat = HazardForecast.concat([haz_fc1, haz_fc2])
-    assert isinstance(haz_fc_concat, HazardForecast)
-    npt.assert_array_equal(
-        haz_fc_concat.lead_time, np.concatenate([lead_time, lead_time])
-    )
-    npt.assert_array_equal(haz_fc_concat.member, np.concatenate([member, member]))
+class TestHazardForecastConcat:
+
+    def test_concat(self, haz_fc, lead_time, member, haz_kwargs):
+        haz_fc1 = haz_fc.select(event_id=[3])
+        haz_fc2 = HazardForecast(
+            haz_type=haz_kwargs["haz_type"], frequency_unit=haz_kwargs["frequency_unit"]
+        )  # Empty hazard
+        haz_fc3 = haz_fc.select(event_id=[1, 2])
+        haz_fc_concat = HazardForecast.concat([haz_fc1, haz_fc2, haz_fc3])
+        assert isinstance(haz_fc_concat, HazardForecast)
+        assert haz_fc_concat.size == 3
+        npt.assert_array_equal(
+            haz_fc_concat.lead_time, np.concatenate((lead_time[2:3], lead_time[0:2]))
+        )
+        npt.assert_array_equal(
+            haz_fc_concat.member, np.concatenate((member[2:3], member[0:2]))
+        )
+        npt.assert_array_equal(haz_fc_concat.event_id, [3, 1, 2])
+
+    def test_empty_list(self):
+        haz_concat = HazardForecast.concat([])
+        assert isinstance(haz_concat, HazardForecast)
+        assert haz_concat.size == 0
+        npt.assert_array_equal(haz_concat.lead_time, [])
+        npt.assert_array_equal(haz_concat.event_id, [])
+
+    def test_type_fail(self, haz_fc, hazard):
+        with pytest.raises(TypeError, match="different classes"):
+            HazardForecast.concat([haz_fc, hazard])
+        with pytest.raises(TypeError, match="different classes"):
+            Hazard.concat([haz_fc, hazard])
 
 
 class TestSelect:

climada/util/forecast.py

@@ -52,9 +52,13 @@ def __init__(
         """
 
         self.lead_time = (
-            np.asarray(lead_time) if lead_time is not None else np.array([])
+            np.asarray(lead_time)
+            if lead_time is not None
+            else np.array([], dtype="timedelta64[ns]")
+        )
+        self.member = (
+            np.asarray(member) if member is not None else np.array([], dtype="int")
         )
-        self.member = np.asarray(member) if member is not None else np.array([])
         super().__init__(**kwargs)
 
     def idx_member(self, member: np.ndarray) -> np.ndarray: