Add option to not overwrite existing flags to concatFlags

CHANGELOG.md

@@ -9,6 +9,7 @@ SPDX-License-Identifier: GPL-3.0-or-later
 ## Unreleased
 [List of commits](https://git.ufz.de/rdm-software/saqc/-/compare/v2.2.1...develop)
 ### Added
+- add option to not overwrite existing flags to `concatFlags`
 ### Changed
 ### Removed
 ### Fixed

saqc/funcs/resampling.py

@@ -334,9 +334,10 @@ class ResamplingMixin:
             "inverse_interpolation",
             "match",
         ] = "match",
-        freq: Optional[str] = None,
-        drop: Optional[bool] = False,
-        squeeze: Optional[bool] = False,
+        freq: str | None = None,
+        drop: bool = False,
+        squeeze: bool = False,
+        overwrite: bool = True,
         **kwargs,
     ) -> "SaQC":
         """
@@ -394,6 +395,10 @@ class ResamplingMixin:
             If set to `True`, the appended flags frame will be squeezed - resulting in function specific flags informations
             getting lost.
 
+        overwrite: bool, default True
+            If set to True, the newly appended flags will overwrite exsiting flags. This might result in a loss of previous
+            flagging information.
+
         Returns
         -------
         saqc.SaQC
@@ -449,13 +454,19 @@ class ResamplingMixin:
             raise ValueError(f"unknown method {method}")
 
         history = self._flags.history[field].apply(dummy.index, func, func_kws)
+
+        if overwrite is False:
+            mask = _isflagged(self._flags[target], thresh=kwargs["dfilter"])
+            history.hist[mask] = np.nan
+
         if squeeze:
             history = history.squeeze(raw=True)
 
             meta = {
-                "func": f"concatFlags({field})",
-                "args": (field, target),
+                "func": f"concatFlags",
+                "args": (field,),
                 "kwargs": {
+                    "target": target,
                     "method": method,
                     "freq": freq,
                     "drop": drop,

tests/funcs/test_harm_funcs.py → tests/funcs/test_resampling.py

@@ -375,3 +375,55 @@ def test_harmSingleVarInterpolationShift(data, params, expected):
     qc = qc.dropField(h_field)
     assert qc.data[field].equals(pre_data[field])
     assert qc.flags[field].equals(pre_flags[field])
+
+
+def test_concatFlags():
+    index = pd.to_datetime(
+        [
+            "2020-01-01 00:00",
+            "2020-01-01 00:10",
+            "2020-01-01 00:30",
+            "2020-01-01 00:40",
+            "2020-01-01 01:00",
+        ]
+    )
+
+    df = pd.DataFrame(
+        data={
+            "a": [
+                1,
+                2,
+                5,
+                4,
+                3,
+            ]
+        },
+        index=index,
+    )
+
+    qc = SaQC(df)
+
+    qc = qc.flagRange(field="a", max=4)
+
+    # branch out to another variable
+    qc = qc.flagRange(field="a", target="b", max=3)
+
+    # bring the flags back again
+    qc_overwrite = qc.concatFlags("b", target="a", overwrite=True, squeeze=True)
+    hist_overwrite = qc_overwrite._flags.history["a"].hist.astype(float)
+    assert hist_overwrite[0].equals(
+        pd.Series([np.nan, np.nan, 255.0, np.nan, np.nan], index=index)
+    )
+    assert hist_overwrite[1].equals(
+        pd.Series([np.nan, np.nan, 255.0, 255.0, np.nan], index=index)
+    )
+
+    # bring the flags back again
+    qc_respect = qc.concatFlags("b", target="a", overwrite=False, squeeze=True)
+    hist_respect = qc_respect._flags.history["a"].hist.astype(float)
+    assert hist_respect[0].equals(
+        pd.Series([np.nan, np.nan, 255.0, np.nan, np.nan], index=index)
+    )
+    assert hist_respect[1].equals(
+        pd.Series([np.nan, np.nan, np.nan, 255.0, np.nan], index=index)
+    )