feat: Add {Expr,Series}.any_value

docs/api-reference/expr.md

@@ -8,6 +8,7 @@
         - alias
         - all
         - any
+        - any_value
         - cast
         - ceil
         - clip

docs/api-reference/series.md

@@ -11,6 +11,7 @@
         - alias
         - all
         - any
+        - any_value
         - arg_max
         - arg_min
         - arg_true

narwhals/_arrow/group_by.py

@@ -41,6 +41,7 @@ class ArrowGroupBy(EagerGroupBy["ArrowDataFrame", "ArrowExpr", "Aggregation"]):
         "any": "any",
         "first": "first",
         "last": "last",
+        "any_value": "first",
     }
     _REMAP_UNIQUE: ClassVar[Mapping[UniqueKeepStrategy, Aggregation]] = {
         "any": "min",
@@ -52,7 +53,7 @@ class ArrowGroupBy(EagerGroupBy["ArrowDataFrame", "ArrowExpr", "Aggregation"]):
     )
     _OPTION_COUNT_VALID: ClassVar[frozenset[NarwhalsAggregation]] = frozenset(("count",))
     _OPTION_ORDERED: ClassVar[frozenset[NarwhalsAggregation]] = frozenset(
-        ("first", "last")
+        ("first", "last", "any_value")
     )
     _OPTION_VARIANCE: ClassVar[frozenset[NarwhalsAggregation]] = frozenset(("std", "var"))
     _OPTION_SCALAR: ClassVar[frozenset[NarwhalsAggregation]] = frozenset(
@@ -89,11 +90,19 @@ def _configure_agg(
         elif function_name in self._OPTION_SCALAR:
             option = pc.ScalarAggregateOptions(min_count=0)
         elif function_name in self._OPTION_ORDERED:
-            grouped, option = self._ordered_agg(grouped, function_name)
+            ignore_nulls = kwargs.get("ignore_nulls", False)
+            grouped, option = self._ordered_agg(
+                grouped, function_name, ignore_nulls=ignore_nulls
+            )
         return grouped, self._remap_expr_name(function_name), option
 
     def _ordered_agg(
-        self, grouped: pa.TableGroupBy, name: NarwhalsAggregation, /
+        self,
+        grouped: pa.TableGroupBy,
+        name: NarwhalsAggregation,
+        /,
+        *,
+        ignore_nulls: bool,
     ) -> tuple[pa.TableGroupBy, AggregateOptions]:
         """The default behavior of `pyarrow` raises when `first` or `last` are used.
 
@@ -117,7 +126,7 @@ def _ordered_agg(
                 f"See https://github.com/apache/arrow/issues/36709"
             )
             raise NotImplementedError(msg)
-        return grouped, pc.ScalarAggregateOptions(skip_nulls=False)
+        return grouped, pc.ScalarAggregateOptions(skip_nulls=ignore_nulls)
 
     def agg(self, *exprs: ArrowExpr) -> ArrowDataFrame:
         self._ensure_all_simple(exprs)

narwhals/_arrow/series.py

@@ -1104,6 +1104,11 @@ def exp(self) -> Self:
     def sqrt(self) -> Self:
         return self._with_native(pc.sqrt(self.native))
 
+    def any_value(
+        self, *, ignore_nulls: bool, _return_py_scalar: bool = True
+    ) -> PythonLiteral:
+        return self.drop_nulls().first() if ignore_nulls else self.first()
+
     @property
     def dt(self) -> ArrowSeriesDateTimeNamespace:
         return ArrowSeriesDateTimeNamespace(self)

narwhals/_compliant/expr.py

@@ -131,6 +131,7 @@ def broadcast(self) -> Self: ...
     def alias(self, name: str) -> Self: ...
     def all(self) -> Self: ...
     def any(self) -> Self: ...
+    def any_value(self, *, ignore_nulls: bool) -> Self: ...
     def count(self) -> Self: ...
     def min(self) -> Self: ...
     def max(self) -> Self: ...
@@ -824,6 +825,11 @@ def first(self) -> Self:
     def last(self) -> Self:
         return self._reuse_series("last", returns_scalar=True)
 
+    def any_value(self, *, ignore_nulls: bool) -> Self:
+        return self._reuse_series(
+            "any_value", returns_scalar=True, ignore_nulls=ignore_nulls
+        )
+
     @property
     def cat(self) -> EagerExprCatNamespace[Self]:
         return EagerExprCatNamespace(self)

narwhals/_compliant/series.py

@@ -128,6 +128,7 @@ def __rmul__(self, other: Any) -> Self: ...
     def __ror__(self, other: Any) -> Self: ...
     def all(self) -> bool: ...
     def any(self) -> bool: ...
+    def any_value(self, *, ignore_nulls: bool) -> PythonLiteral: ...
     def arg_max(self) -> int: ...
     def arg_min(self) -> int: ...
     def arg_true(self) -> Self: ...

narwhals/_compliant/typing.py

@@ -194,11 +194,11 @@ class ScalarKwargs(TypedDict, total=False):
     "any",
     "first",
     "last",
+    "any_value",
 ]
 """`Expr` methods we aim to support in `DepthTrackingGroupBy`.
 
 Be sure to update me if you're working on one of these:
-- https://github.com/narwhals-dev/narwhals/issues/981
 - https://github.com/narwhals-dev/narwhals/issues/2385
 - https://github.com/narwhals-dev/narwhals/issues/2484
 - https://github.com/narwhals-dev/narwhals/issues/2526

narwhals/_dask/expr.py

@@ -693,6 +693,7 @@ def str(self) -> DaskExprStringNamespace:
     def dt(self) -> DaskExprDateTimeNamespace:
         return DaskExprDateTimeNamespace(self)
 
+    any_value = not_implemented()
     filter = not_implemented()
     first = not_implemented()
     rank = not_implemented()

narwhals/_duckdb/expr.py

@@ -105,6 +105,15 @@ def _first(self, expr: Expression, *order_by: str) -> Expression:
     def _last(self, expr: Expression, *order_by: str) -> Expression:
         return self._first_last("last", expr, order_by)
 
+    def _any_value(self, expr: Expression, *, ignore_nulls: bool) -> Expression:
+        # !NOTE: DuckDB `any_value` returns the first non-null value
+        # See: https://duckdb.org/docs/stable/sql/functions/aggregates#any_valuearg
+        return (
+            self._function("any_value", expr)
+            if ignore_nulls
+            else self._function("first", expr)
+        )
+
     def __narwhals_namespace__(self) -> DuckDBNamespace:  # pragma: no cover
         from narwhals._duckdb.namespace import DuckDBNamespace
 

narwhals/_ibis/expr.py

@@ -127,6 +127,12 @@ def _last(self, expr: ir.Value, *order_by: str) -> ir.Value:
             order_by=self._sort(*order_by), include_null=True
         )
 
+    def _any_value(self, expr: ir.Value, *, ignore_nulls: bool) -> ir.Value:
+        # !NOTE: ibis arbitrary returns a random non-null value
+        # See: https://ibis-project.org/reference/expression-generic.html#ibis.expr.types.generic.Column.arbitrary
+        expr = cast("ir.Column", expr)
+        return expr.arbitrary() if ignore_nulls else expr.first(include_null=True)
+
     def __narwhals_namespace__(self) -> IbisNamespace:  # pragma: no cover
         from narwhals._ibis.namespace import IbisNamespace
 

narwhals/_pandas_like/expr.py

@@ -109,7 +109,13 @@ def window_kwargs_to_pandas_equivalent(  # noqa: C901
             "min_periods": kwargs["min_samples"],
             "ignore_na": kwargs["ignore_nulls"],
         }
-    elif function_name in {"first", "last"}:
+    elif function_name in {"first", "last", "any_value"}:
+        if kwargs.get("ignore_nulls"):
+            msg = (
+                "`Expr.any_value(ignore_nulls=True)` is not supported in a `over` "
+                "context for pandas-like backend."
+            )
+            raise NotImplementedError(msg)
         pandas_kwargs = {
             "n": _REMAP_ORDERED_INDEX[cast("NarwhalsAggregation", function_name)]
         }
@@ -357,17 +363,16 @@ def func(df: PandasLikeDataFrame) -> Sequence[PandasLikeSeries]:  # noqa: C901,
                     msg = "Safety check failed, please report a bug."
                     raise AssertionError(msg)
                 res_native = grouped.transform("size").to_frame(aliases[0])
-            elif function_name in {"first", "last"}:
+            elif function_name in {"first", "last", "any_value"}:
                 with warnings.catch_warnings():
                     # Ignore settingwithcopy warnings/errors, they're false-positives here.
                     warnings.filterwarnings("ignore", message="\n.*copy of a slice")
-                    _nth = getattr(
+                    _agg = getattr(
                         grouped[[*partition_by, *aliases]], pandas_function_name
                     )(**pandas_kwargs)
-                _nth.reset_index(drop=True, inplace=True)
-                res_native = df.native[list(partition_by)].merge(
-                    _nth, on=list(partition_by)
-                )[list(aliases)]
+                _agg.reset_index(drop=True, inplace=True)
+                keys = list(partition_by)
+                res_native = df.native[keys].merge(_agg, on=keys)[list(aliases)]
             else:
                 res_native = grouped[list(aliases)].transform(
                     pandas_function_name, **pandas_kwargs

narwhals/_pandas_like/group_by.py

@@ -62,6 +62,7 @@
 _REMAP_ORDERED_INDEX: Mapping[NarwhalsAggregation, Literal[0, -1]] = {
     "first": 0,
     "last": -1,
+    "any_value": 0,
 }
 
 
@@ -151,7 +152,7 @@ def _getitem_aggs(
                     for col in cols
                 ]
             )
-        elif self.is_last() or self.is_first():
+        elif self.is_last() or self.is_first() or self.is_any_value():
             result = self.native_agg()(group_by._grouped[[*group_by._keys, *names]])
             result.set_index(group_by._keys, inplace=True)  # noqa: PD002
         else:
@@ -175,6 +176,9 @@ def is_first(self) -> bool:
     def is_mode(self) -> bool:
         return self.leaf_name == "mode"
 
+    def is_any_value(self) -> bool:
+        return self.leaf_name == "any_value"
+
     def is_top_level_function(self) -> bool:
         # e.g. `nw.len()`.
         return len(list(self.expr._metadata.op_nodes_reversed())) == 1
@@ -191,6 +195,12 @@ def native_agg(self) -> _NativeAgg:
         native_name = PandasLikeGroupBy._remap_expr_name(self.leaf_name)
         last_node = next(self.expr._metadata.op_nodes_reversed())
         if self.leaf_name in _REMAP_ORDERED_INDEX:
+            if last_node.kwargs.get("ignore_nulls"):
+                msg = (
+                    "`Expr.any_value(ignore_nulls=True)` is not supported in a `group_by` "
+                    "context for pandas-like backend"
+                )
+                raise NotImplementedError(msg)
             return methodcaller("nth", n=_REMAP_ORDERED_INDEX[self.leaf_name])
         return _native_agg(native_name, **last_node.kwargs)
 
@@ -215,6 +225,7 @@ class PandasLikeGroupBy(
         "any": "any",
         "first": "nth",
         "last": "nth",
+        "any_value": "nth",
     }
     _original_columns: tuple[str, ...]
     """Column names *prior* to any aliasing in `ParseKeysGroupBy`."""

narwhals/_pandas_like/series.py

@@ -1152,6 +1152,9 @@ def exp(self) -> Self:
     def sqrt(self) -> Self:
         return self._with_native(self.native.pow(0.5))
 
+    def any_value(self, *, ignore_nulls: bool) -> PythonLiteral:
+        return self.drop_nulls().first() if ignore_nulls else self.first()
+
     @property
     def str(self) -> PandasLikeSeriesStringNamespace:
         return PandasLikeSeriesStringNamespace(self)

narwhals/_polars/expr.py

@@ -299,6 +299,9 @@ def mode(self, *, keep: ModeKeepStrategy) -> Self:
         result = self.native.mode()
         return self._with_native(result.first() if keep == "any" else result)
 
+    def any_value(self, *, ignore_nulls: bool) -> Self:
+        return self.drop_nulls().first() if ignore_nulls else self.first()
+
     @property
     def dt(self) -> PolarsExprDateTimeNamespace:
         return PolarsExprDateTimeNamespace(self)

narwhals/_polars/series.py

@@ -664,6 +664,9 @@ def last(self) -> PythonLiteral:
             return self.native.item(-1) if len(self) else None
         return self.native.last()  # type: ignore[return-value]
 
+    def any_value(self, *, ignore_nulls: bool) -> PythonLiteral:
+        return self.drop_nulls().first() if ignore_nulls else self.first()
+
     @property
     def dt(self) -> PolarsSeriesDateTimeNamespace:
         return PolarsSeriesDateTimeNamespace(self)

narwhals/_spark_like/expr.py

@@ -112,6 +112,9 @@ def _last(self, expr: Column, *order_by: str) -> Column:  # pragma: no cover
         msg = "`last` is not supported for PySpark."
         raise NotImplementedError(msg)
 
+    def _any_value(self, expr: Column, *, ignore_nulls: bool) -> Column:
+        return self._F.any_value(expr, ignoreNulls=ignore_nulls)
+
     def broadcast(self) -> Self:
         return self.over([self._F.lit(1)], [])
 

narwhals/_sql/expr.py

@@ -188,6 +188,7 @@ def _coalesce(self, *expr: NativeExprT) -> NativeExprT:
     def _count_star(self) -> NativeExprT: ...
     def _first(self, expr: NativeExprT, *order_by: str) -> NativeExprT: ...
     def _last(self, expr: NativeExprT, *order_by: str) -> NativeExprT: ...
+    def _any_value(self, expr: NativeExprT, *, ignore_nulls: bool) -> NativeExprT: ...
 
     def _when(
         self,
@@ -759,6 +760,11 @@ def func(
 
         return self._with_window_function(func)
 
+    def any_value(self, *, ignore_nulls: bool) -> Self:
+        return self._with_callable(
+            lambda expr: self._any_value(expr, ignore_nulls=ignore_nulls)
+        )
+
     def rank(self, method: RankMethod, *, descending: bool) -> Self:
         if method in {"min", "max", "average"}:
             func = self._function("rank")

narwhals/expr.py

@@ -2368,6 +2368,40 @@ def is_close(  # noqa: PLR0914
 
         return result
 
+    def any_value(self, *, ignore_nulls: bool = False) -> Self:
+        """Get a random value from the column.
+
+        Arguments:
+            ignore_nulls: Whether to ignore null values or not.
+                If `True` and there are no not-null elements, then `None` is returned.
+
+        Examples:
+            >>> import pandas as pd
+            >>> import narwhals as nw
+            >>> data = {"a": [1, 1, 2, 2], "b": [None, "foo", "baz", None]}
+            >>> df_native = pd.DataFrame(data)
+            >>> df = nw.from_native(df_native)
+            >>> df.select(nw.all().any_value(ignore_nulls=False))
+            ┌──────────────────┐
+            |Narwhals DataFrame|
+            |------------------|
+            |       a     b    |
+            |    0  1  None    |
+            └──────────────────┘
+
+            >>> df.group_by("a").agg(nw.col("b").any_value(ignore_nulls=True))
+            ┌──────────────────┐
+            |Narwhals DataFrame|
+            |------------------|
+            |       a     b    |
+            |    0  1   foo    |
+            |    1  2   baz    |
+            └──────────────────┘
+        """
+        return self._append_node(
+            ExprNode(ExprKind.AGGREGATION, "any_value", ignore_nulls=ignore_nulls)
+        )
+
     @property
     def str(self) -> ExprStringNamespace[Self]:
         return ExprStringNamespace(self)

narwhals/series.py

@@ -2844,6 +2844,23 @@ def is_close(
         result = result.rename(orig_name) if name_is_none else result
         return cast("Self", result)
 
+    def any_value(self, *, ignore_nulls: bool = False) -> PythonLiteral:
+        """Get a random value from the column.
+
+        Arguments:
+            ignore_nulls: Whether to ignore null values or not.
+                If `True` and there are no not-null elements, then `None` is returned.
+
+        Examples:
+            >>> import pyarrow as pa
+            >>> import narwhals as nw
+            >>> s_native = pa.chunked_array([[1, 2, None]])
+            >>> s = nw.from_native(s_native, series_only=True)
+            >>> s.any_value(ignore_nulls=True)
+            1
+        """
+        return self._compliant_series.any_value(ignore_nulls=ignore_nulls)
+
     @property
     def str(self) -> SeriesStringNamespace[Self]:
         return SeriesStringNamespace(self)