add api reference index

mkdocs.yml

@@ -13,6 +13,7 @@ nav:
   - Roadmap: roadmap.md
   - Related projects: related.md
   - API Reference:
+    - api-reference/index.md
     - api-reference/narwhals.md
     - api-reference/dataframe.md
     - api-reference/lazyframe.md
@@ -25,6 +26,7 @@ theme:
     - content.code.copy
     - content.code.annotate
     - navigation.footer
+    - navigation.indexes
 plugins:
 - search
 - mkdocstrings:

narwhals/_pandas_like/series.py

@@ -257,6 +257,14 @@ def mean(self) -> Any:
         ser = self._series
         return ser.mean()
 
+    def std(
+        self,
+        *,
+        correction: float = 1.0,
+    ) -> Any:
+        ser = self._series
+        return ser.std(ddof=correction)
+
     def len(self) -> Any:
         return len(self._series)
 

narwhals/series.py

@@ -83,6 +83,12 @@ def cast(
             self._series.cast(translate_dtype(self.__narwhals_namespace__(), dtype))
         )
 
+    def mean(self) -> Any:
+        return self._series.mean()
+
+    def std(self) -> Any:
+        return self._series.std()
+
     def is_in(self, other: Any) -> Self:
         return self._from_series(self._series.is_in(self._extract_native(other)))
 

tests/test_series.py

@@ -52,6 +52,12 @@ def test_dtype(df_raw: Any) -> None:
     assert result.is_numeric()
 
 
+@pytest.mark.parametrize("df_raw", [df_pandas, df_lazy])
+def test_reductions(df_raw: Any) -> None:
+    assert nw.LazyFrame(df_raw).collect()["a"].mean() == 2.0
+    assert nw.LazyFrame(df_raw).collect()["a"].std() == 1.0
+
+
 @pytest.mark.parametrize("df_raw", [df_pandas, df_lazy])
 def test_convert(df_raw: Any) -> None:
     result = nw.LazyFrame(df_raw).collect()["a"].to_numpy()