Fix leading nans bug in _aggregate (#245)

* fix and test

* changelog

* rst rendering

* rerun notebook

* mention notebook and set changelog date

Author: kandersolar

docs/degradation_and_soiling_example.ipynb

@@ -1,6 +1,7 @@
 RdTools Change Log
 ==================
 
+.. include:: changelog/v2.0.4.rst
 .. include:: changelog/v2.0.3.rst
 .. include:: changelog/v2.0.2.rst
 .. include:: changelog/v2.0.1.rst

docs/sphinx/source/changelog.rst

@@ -0,0 +1,14 @@
+*************************
+v2.0.4 (December 4, 2020)
+*************************
+
+Bug Fixes
+---------
+* Fix bug related to leading NaN values with
+  :py:func:`~rdtools.normalization.energy_from_power`. This fixed a small
+  normalization error in ``degradation_and_soiling_example.ipynb`` and
+  slightly changed the clear-sky degradation results (:issue:`244`, :pull:`245`)
+
+Contributors
+------------
+* Kevin Anderson (:ghuser:`kanderso-nrel`)

docs/sphinx/source/changelog/v2.0.4.rst

@@ -620,6 +620,9 @@ def _aggregate(time_series, target_frequency, max_timedelta, series_type):
     max_interval_nanoseconds = max_timedelta.total_seconds() * 10.0**9
 
     gap_mask = t_diffs > max_interval_nanoseconds
+    if time_series.index[0] != union_index[0]:
+        # mask leading NaNs
+        gap_mask[:time_series.index[0]] = True
 
     time_series = time_series.reindex(union_index)
     t_diffs = np.diff(time_series.index.astype('int64').values)

rdtools/normalization.py

@@ -99,3 +99,12 @@ def test_energy_from_power_single_value_with_target():
     expected_result = pd.Series([100.], index=times, name='energy_Wh')
     result = energy_from_power(power, target_frequency='H')
     pd.testing.assert_series_equal(result, expected_result)
+
+def test_energy_from_power_leading_nans():
+    # GH 244
+    power = pd.Series(1, pd.date_range('2019-01-01', freq='15min', periods=5))
+    power.iloc[:2] = np.nan
+    expected_result = pd.Series([np.nan, np.nan, 0.25, 0.25],
+                                index=power.index[1:], name='energy_Wh')
+    result = energy_from_power(power)
+    pd.testing.assert_series_equal(result, expected_result)