parse names only

narwhals/_arrow/dataframe.py

@@ -764,15 +764,24 @@ def sample(
 
     def unpivot(
         self: Self,
-        on: list[str] | None,
-        index: list[str],
+        on: str | list[str] | None,
+        index: str | list[str] | None,
         variable_name: str,
         value_name: str,
     ) -> Self:
         native_frame = self._native_frame
         n_rows = len(self)
 
-        on_ = [c for c in self.columns if c not in index] if on is None else on
+        index_: list[str] = (
+            [] if index is None else [index] if isinstance(index, str) else index
+        )
+        on_: list[str] = (
+            [c for c in self.columns if c not in index_]
+            if on is None
+            else [on]
+            if isinstance(on, str)
+            else on
+        )
 
         promote_kwargs = (
             {"promote_options": "permissive"}
@@ -784,11 +793,11 @@ def unpivot(
                 [
                     pa.Table.from_arrays(
                         [
-                            *[native_frame.column(idx_col) for idx_col in index],
+                            *[native_frame.column(idx_col) for idx_col in index_],
                             pa.array([on_col] * n_rows, pa.string()),
                             native_frame.column(on_col),
                         ],
-                        names=[*index, variable_name, value_name],
+                        names=[*index_, variable_name, value_name],
                     )
                     for on_col in on_
                 ],

narwhals/_dask/dataframe.py

@@ -417,8 +417,8 @@ def gather_every(self: Self, n: int, offset: int) -> Self:
 
     def unpivot(
         self: Self,
-        on: list[str] | None,
-        index: list[str],
+        on: str | list[str] | None,
+        index: str | list[str] | None,
         variable_name: str,
         value_name: str,
     ) -> Self:

narwhals/_duckdb/dataframe.py

@@ -429,11 +429,22 @@ def drop_nulls(self: Self, subset: list[str] | None) -> Self:
 
     def unpivot(
         self: Self,
-        on: list[str] | None,
-        index: list[str],
+        on: str | list[str] | None,
+        index: str | list[str] | None,
         variable_name: str,
         value_name: str,
     ) -> Self:
+        index_: list[str] = (
+            [] if index is None else [index] if isinstance(index, str) else index
+        )
+        on_: list[str] = (
+            [c for c in self.columns if c not in index_]
+            if on is None
+            else [on]
+            if isinstance(on, str)
+            else on
+        )
+
         if variable_name == "":
             msg = "`variable_name` cannot be empty string for duckdb backend."
             raise NotImplementedError(msg)
@@ -442,10 +453,8 @@ def unpivot(
             msg = "`value_name` cannot be empty string for duckdb backend."
             raise NotImplementedError(msg)
 
-        on_ = [c for c in self.columns if c not in index] if on is None else on
-
         cols_to_select = ", ".join(
-            f'"{col}"' for col in [*index, variable_name, value_name]
+            f'"{col}"' for col in [*index_, variable_name, value_name]
         )
         unpivot_on = ", ".join(f'"{col}"' for col in on_)
 

narwhals/_pandas_like/dataframe.py

@@ -1057,17 +1057,17 @@ def sample(
 
     def unpivot(
         self: Self,
-        on: list[str] | None,
-        index: list[str],
+        on: str | list[str] | None,
+        index: str | list[str] | None,
         variable_name: str,
         value_name: str,
     ) -> Self:
         return self._from_native_frame(
             self._native_frame.melt(
                 id_vars=index,
                 value_vars=on,
-                var_name=variable_name if variable_name is not None else "variable",
-                value_name=value_name if value_name is not None else "value",
+                var_name=variable_name,
+                value_name=value_name,
             )
         )
 

narwhals/_polars/dataframe.py

@@ -310,8 +310,8 @@ def drop(self: Self, columns: list[str], strict: bool) -> Self:  # noqa: FBT001
 
     def unpivot(
         self: Self,
-        on: list[str] | None,
-        index: list[str],
+        on: str | list[str] | None,
+        index: str | list[str] | None,
         variable_name: str,
         value_name: str,
     ) -> Self:
@@ -506,8 +506,8 @@ def drop(self: Self, columns: list[str], strict: bool) -> Self:  # noqa: FBT001
 
     def unpivot(
         self: Self,
-        on: list[str] | None,
-        index: list[str],
+        on: str | list[str] | None,
+        index: str | list[str] | None,
         variable_name: str,
         value_name: str,
     ) -> Self:

narwhals/_spark_like/dataframe.py

@@ -412,8 +412,8 @@ def explode(self: Self, columns: str | Sequence[str], *more_columns: str) -> Sel
 
     def unpivot(
         self: Self,
-        on: list[str] | None,
-        index: list[str],
+        on: str | list[str] | None,
+        index: str | list[str] | None,
         variable_name: str,
         value_name: str,
     ) -> Self:

narwhals/dataframe.py

@@ -330,22 +330,13 @@ def unpivot(
         variable_name: str | None,
         value_name: str | None,
     ) -> Self:
-        on_ = [on] if isinstance(on, str) else on
-        index_ = (
-            [index]
-            if isinstance(index, str)
-            else index
-            if isinstance(index, list)
-            else []
-        )
-
         variable_name = variable_name if variable_name is not None else "variable"
         value_name = value_name if value_name is not None else "value"
 
         return self._from_compliant_dataframe(
             self._compliant_frame.unpivot(
-                on=on_,
-                index=index_,
+                on=on,
+                index=index,
                 variable_name=variable_name,
                 value_name=value_name,
             )