do not assign not-given variable names implicitly

README.md

@@ -30,9 +30,9 @@
 - `flag_values`:
   + Number
   + if a value is flagged, so are the next n previously unflagged values
-- `assign_to`:
-  + String
-  + Assign the test result to a new columns given as a value to assign
+- `assign`:
+  + boolean
+  + Assign the test result to a new column
 ### Predefined Tests
 
 | name  | required parameters | optional parameters | description                             |

core.py

@@ -16,7 +16,7 @@ class FlagParams:
     FLAG = "flag"
     PERIODE = "flag_period"
     VALUES = "flag_values"
-    ASSIGN = "assign_to"
+    ASSIGN = "assign"
 
 
 def _inferFrequency(data):
@@ -74,14 +74,13 @@ def runner(meta, flagger, data, flags=None, nodata=np.nan):
             if pd.isnull(flag_test):
                 continue
 
+            varname, start_date, end_date = configrow[fields]
             func_name, flag_params = parseFlag(flag_test)
 
-            assign_to = flag_params.get(FlagParams.ASSIGN)
-            if assign_to:
-                dummy = pd.DataFrame(index=data.index, columns=[assign_to])
-                flags = flags.join(flagger.emptyFlags(dummy))
+            if flag_params.get(FlagParams.ASSIGN):
+                dummy = pd.DataFrame(index=data.index, columns=[varname])
+                flags[varname] = flagger.emptyFlags(dummy)
 
-            varname, start_date, end_date = configrow[fields]
             if varname not in data:
                 continue