Fix stata saving (#624)

close #618

mlem/contrib/pandas.py

@@ -305,6 +305,11 @@ def has_index(df: pd.DataFrame):
     return not isinstance(df.index, pd.RangeIndex)
 
 
+def has_named_index(df: pd.DataFrame):
+    """Returns true if all index columns are named"""
+    return df.index.name or all(df.index.names)
+
+
 def _reset_index(df: pd.DataFrame):
     """Transforms indexes to columns"""
     index_name = df.index.name or ""  # save it for future renaming
@@ -459,8 +464,19 @@ def write(
             write_kwargs.update(self.write_args)
         write_kwargs.update(kwargs)
 
+        # sometimes index may be consumed by model or used at feature engineering step,
+        # so we keep it instead of dropping if it's non-trivial
         if has_index(df):
-            df = reset_index(df)
+            if PANDAS_FORMATS[
+                "stata"
+            ].write_func == self.write_func and not has_named_index(df):
+                logging.info(
+                    "Stata format doesn't allow saving columns with empty names, so you must name the index."
+                    "Use `df.index.name = 'index'` to name it or df.reset_index(drop=True) to drop it instead."
+                )
+                df = df.reset_index(drop=True)
+            else:
+                df = reset_index(df)
 
         with storage.open(path) as (f, art):
             if self.string_buffer:

tests/contrib/test_pandas.py

@@ -10,6 +10,7 @@
 import pytest
 from fsspec.implementations.local import LocalFileSystem
 from pydantic import parse_obj_as
+from pytest_lazyfixture import lazy_fixture
 from sklearn.datasets import load_iris
 from sklearn.model_selection import train_test_split
 
@@ -27,6 +28,7 @@
     PandasWriter,
     SeriesType,
     get_pandas_batch_formats,
+    has_index,
     pd_type_from_string,
     python_type_from_pd_string_repr,
     python_type_from_pd_type,
@@ -510,6 +512,20 @@ def test_import_data_csv(tmpdir, write_csv, file_ext, type_, data):
     _check_data(meta, target_path)
 
 
+def test_import_data_stata(tmpdir, data):
+    path = str(tmpdir / "mydata.stata")
+    data.to_stata(path, write_index=False)
+    meta = import_object(
+        path, target=path, type_="pandas[stata]", copy_data=True
+    )
+    pandas_assert(
+        data.astype(
+            "int32"
+        ),  # TODO: int32 converts to int64 for some reason for stata
+        meta.get_value(),
+    )
+
+
 @long
 def test_import_data_csv_remote(s3_tmp_path, s3_storage_fs, write_csv):
     project_path = s3_tmp_path("test_csv_import")
@@ -619,6 +635,28 @@ def f(x):
     assert set(get_object_requirements(sig).modules) == {"pandas"}
 
 
+@pytest.mark.parametrize(
+    "df",
+    [
+        lazy_fixture("data"),
+        lazy_fixture("data2"),
+    ],
+)
+def test_does_not_have_index(df):
+    assert not has_index(df)
+
+
+@pytest.mark.parametrize(
+    "df",
+    [
+        PD_DATA_FRAME_INDEX,
+        PD_DATA_FRAME_MULTIINDEX,
+    ],
+)
+def test_has_index(df):
+    assert has_index(df)
+
+
 # Copyright 2019 Zyfra
 # Copyright 2021 Iterative
 #