fixing some linting and mypy errors

src/onemod/io/base.py

@@ -164,7 +164,7 @@ def check_exists(
         FIXME: Assumes pipeline has been built (so paths are absolute)
 
         """
-        item_names = item_names or self.items.keys()
+        item_names = item_names or set(self.items.keys())
         upstream_stages = upstream_stages or self.dependencies
 
         missing_items = {}

src/onemod/utils/subsets.py

@@ -4,24 +4,12 @@
 import polars as pl
 
 
-# def create_subsets(groupby: set[str], lf: pl.LazyFrame) -> pl.DataFrame:
-#     """Create subsets from groupby."""
-#     subsets = (
-#         lf.select(list(groupby))
-#         .unique()
-#         .with_row_index(name="subset_id")
-#         .collect()
-#     )
-
-#     return subsets
-
-
 def create_subsets(groupby: set[str], data: pd.DataFrame) -> pd.DataFrame:
     """Create subsets from groupby."""
     sorted_groupby = sorted(groupby)
     groups = data.groupby(sorted_groupby)
     subsets = pd.DataFrame(
-        [subset for subset in groups.groups.keys()], columns=groups.keys
+        [subset for subset in groups.groups.keys()], columns=sorted_groupby
     )
     subsets.sort_values(by=sorted_groupby)
     subsets["subset_id"] = subsets.index