From f08893760b1626493027440c9b4d4f329425ec37 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?thorbjoernl=20=28Thorbj=C3=B8rn=29?=
 <51087536+thorbjoernl@users.noreply.github.com>
Date: Fri, 23 Aug 2024 12:01:44 +0000
Subject: [PATCH] Undo right-shifting

---
 pyaerocom/stats/mda8/mda8.py  |  9 ++-------
 tests/stats/mda8/test_mda8.py | 21 ++++++++++-----------
 2 files changed, 12 insertions(+), 18 deletions(-)

diff --git a/pyaerocom/stats/mda8/mda8.py b/pyaerocom/stats/mda8/mda8.py
index 88e118f99..99ce4bbe4 100644
--- a/pyaerocom/stats/mda8/mda8.py
+++ b/pyaerocom/stats/mda8/mda8.py
@@ -100,13 +100,8 @@ def _calc_mda8(data: xr.DataArray) -> xr.DataArray:
 
 
 def _rolling_average_8hr(arr: xr.DataArray) -> xr.DataArray:
-    # Xarray labels the data left, while we want it to be labeled right, so we add 8h to
-    # the time index.
-    new_arr = arr.rolling(time=8, min_periods=6).mean()
-    # Xarray labels the data left, while we want it to be labeled right, so we add 8h to
-    # the time index.
-    new_arr["time"] = new_arr.get_index("time") + pd.Timedelta("8h")
-    return new_arr
+    # Xarray labels the data right based on the last data point in the period for rolling.
+    return arr.rolling(time=8, center=False, min_periods=6).mean()
 
 
 def _daily_max(arr: xr.DataArray) -> xr.DataArray:
diff --git a/tests/stats/mda8/test_mda8.py b/tests/stats/mda8/test_mda8.py
index 707a727d2..d81fb8294 100644
--- a/tests/stats/mda8/test_mda8.py
+++ b/tests/stats/mda8/test_mda8.py
@@ -1,7 +1,6 @@
 import numpy as np
 import pytest
 import xarray as xr
-import pandas as pd
 
 from pyaerocom.colocation.colocated_data import ColocatedData
 from pyaerocom.stats.mda8.mda8 import (
@@ -27,13 +26,13 @@ def test_data(time, values) -> xr.DataArray:
         pytest.param(
             xr.date_range(start="2024-01-01 01:00", periods=49, freq="1h"),
             [0.0] * 49,
-            [np.nan, 0, np.nan],
+            [0, 0, np.nan],
             id="zeros",
         ),
         pytest.param(
             xr.date_range(start="2024-01-01 01:00", periods=49, freq="1h"),
             np.linspace(start=1, stop=49, num=49),
-            [np.nan, 36.5, np.nan],
+            [20.5, 44.5, np.nan],
             id="incrementing-by-1",
         ),
         pytest.param(
@@ -54,7 +53,7 @@ def test_data(time, values) -> xr.DataArray:
         pytest.param(
             xr.date_range(start="2024-01-01 06:00:00", periods=30, freq="1h"),
             np.arange(30),
-            [np.nan, 25.5],
+            [np.nan, np.nan],
             id="#1323",
         ),
     ),
@@ -98,17 +97,17 @@ def test_coldata_to_mda8(coldata):
     assert mda8.shape == (2, 8, 1)
 
     assert mda8.data.values[0, :, 0] == pytest.approx(
-        [np.nan, np.nan, 1.18853785, 1.18604125, 1.18869106, 1.18879322, 1.18807846, 1.18700801],
+        [np.nan, np.nan, 1.18741556, 1.18777241, 1.18869106, 1.18879322, 1.18807846, 1.18700801],
         abs=10**-5,
         nan_ok=True,
     )
 
     assert mda8.data.values[1, :, 0] == pytest.approx(
         [
-            np.nan,
+            1.57327333,
             1.28884431,
-            1.28853785,
-            1.28604125,
+            1.28741556,
+            1.28777241,
             1.28869106,
             1.28879322,
             1.28807846,
@@ -156,7 +155,8 @@ def test_rollingaverage(test_data, exp_ravg):
 def test_rollingaverage_label():
     """
     Checks that the labels of rolling average is correct (we want it to be labeled based
-    on the "right-most" interval, ie. latest measurement in the interval).
+    on the "right-most" interval, ie. latest measurement in the interval). This is currently
+    the case in xarray but not greatly documented, so this test checks for that.
 
     https://github.com/metno/pyaerocom/issues/1323
     """
@@ -169,8 +169,7 @@ def test_rollingaverage_label():
     ravg = _rolling_average_8hr(data)
 
     assert np.all(
-        ravg.get_index("time")
-        == xr.date_range(start="2024-01-01 00:00", periods=24, freq="1h") + pd.Timedelta("8h")
+        ravg.get_index("time") == xr.date_range(start="2024-01-01 00:00", periods=24, freq="1h")
     )