old polars

narwhals-dev · Oct 7, 2024 · f0777c6 · f0777c6
1 parent f5812e4
commit f0777c6
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Showing 2 changed files with 8 additions and 2 deletions.
diff --git a/narwhals/_pandas_like/series.py b/narwhals/_pandas_like/series.py
@@ -653,7 +653,8 @@ def to_dummies(
             prefix=name,
             prefix_sep=separator,
             drop_first=drop_first,
-            dummy_na=has_nulls,  # Adds a null column at the end, even if there aren't any.
+            # Adds a null column at the end, depending on whether or not there are any.
+            dummy_na=has_nulls,
             dtype=int,
         )
         if has_nulls:

diff --git a/narwhals/_polars/series.py b/narwhals/_polars/series.py
@@ -185,8 +185,13 @@ def to_dummies(
         from narwhals._polars.dataframe import PolarsDataFrame
 
         if self._backend_version < (0, 20, 15):  # pragma: no cover
+            has_nulls = self._native_series.is_null().any()
             result = self._native_series.to_dummies(separator=separator)
-            result = result.select(result.columns[int(drop_first) :])
+            output_columns = result.columns
+            if drop_first:
+                _ = output_columns.pop(int(has_nulls))
+
+            result = result.select(output_columns)
         else:
             result = self._native_series.to_dummies(
                 separator=separator, drop_first=drop_first