David Schäfer · David Schäfer
--- a/saqc/core/core.py
+++ b/saqc/core/core.py
            raise AttributeError(f"SaQC has no attribute {repr(key)}")
        return partial(FUNC_MAP[key], self)

+    def __getitem__(self, key: str | Sequence[str] | slice) -> SaQC:
+
+        if isinstance(key, slice):
+            key = self._data.columns.to_list()
+        keys = toSequence(key)
+
+        return self._construct(_data=self._data[keys], _flags=self._flags.select(keys))
+
+    def __setitem__(self, key: str | Sequence[str] | slice, obj: SaQC) -> None:
+
+        if isinstance(key, slice):
+            key = self._data.columns.to_list()
-        if isinstance(key, slice):
-            key = self._data.columns.to_list()
+        if isinstance(key, slice): 
+            if key == slice(None):
+                key = self._data.columns.to_list()
+            else:
+                raise KeyError("only `slice(None)` aka. `obj[:]` is supported")
--- a/saqc/core/core.py
+++ b/saqc/core/core.py
+    def __setitem__(self, key: str | Sequence[str] | slice, obj: SaQC) -> None:
+
+        if isinstance(key, slice):
+            key = self._data.columns.to_list()
+
+        lkeys = toSequence(key)
+        rkeys = obj._data.columns
+        if len(lkeys) != len(rkeys):
+            raise ValueError(
+                f"cannot set value object with {len(rkeys)} fields to indexing result of {len(lkeys)} fields"
+            )
+
+        for lkey, rkey in zip(lkeys, rkeys):
+            self._data[lkey] = obj._data[rkey]
+            self._flags[lkey] = obj._flags[rkey]
+            self._flags.history[lkey] = obj._flags.history[rkey]