is-finite for eager

docs/api-reference/expr.md

@@ -21,6 +21,7 @@
         - clip
         - is_between
         - is_duplicated
+        - is_finite
         - is_first_distinct
         - is_in
         - is_last_distinct

docs/api-reference/series.md

@@ -26,6 +26,7 @@
         - is_between
         - is_duplicated
         - is_empty
+        - is_finite
         - is_first_distinct
         - is_in
         - is_last_distinct

narwhals/_arrow/expr.py

@@ -372,6 +372,9 @@ def func(df: ArrowDataFrame) -> list[ArrowSeries]:
     def mode(self: Self) -> Self:
         return reuse_series_implementation(self, "mode")
 
+    def is_finite(self: Self) -> Self:
+        return reuse_series_implementation(self, "is_finite")
+
     @property
     def dt(self: Self) -> ArrowExprDateTimeNamespace:
         return ArrowExprDateTimeNamespace(self)

narwhals/_arrow/series.py

@@ -721,6 +721,11 @@ def mode(self: Self) -> ArrowSeries:
             plx.col(col_token) == plx.col(col_token).max()
         )[self.name]
 
+    def is_finite(self: Self) -> Self:
+        import pyarrow.compute as pc  # ignore-banned-import
+
+        return self._from_native_series(pc.is_finite(self._native_series))
+
     def __iter__(self: Self) -> Iterator[Any]:
         yield from self._native_series.__iter__()
 

narwhals/_pandas_like/expr.py

@@ -387,6 +387,9 @@ def gather_every(self: Self, n: int, offset: int = 0) -> Self:
     def mode(self: Self) -> Self:
         return reuse_series_implementation(self, "mode")
 
+    def is_finite(self: Self) -> Self:
+        return reuse_series_implementation(self, "is_finite")
+
     @property
     def str(self: Self) -> PandasLikeExprStringNamespace:
         return PandasLikeExprStringNamespace(self)

narwhals/_pandas_like/series.py

@@ -686,6 +686,11 @@ def mode(self: Self) -> Self:
     def __iter__(self: Self) -> Iterator[Any]:
         yield from self._native_series.__iter__()
 
+    def is_finite(self: Self) -> Self:
+        import numpy as np  # ignore-banned-import
+
+        return self._from_native_series(np.isfinite(self._native_series))
+
     @property
     def str(self) -> PandasLikeSeriesStringNamespace:
         return PandasLikeSeriesStringNamespace(self)

narwhals/expr.py

@@ -2313,6 +2313,57 @@ def mode(self: Self) -> Self:
         """
         return self.__class__(lambda plx: self._call(plx).mode())
 
+    def is_finite(self: Self) -> Self:
+        """
+        Returns a boolean Series indicating which values are finite.
+
+        Returns:
+            Expression of `Boolean` data type.
+
+        Examples:
+            >>> import narwhals as nw
+            >>> import pandas as pd
+            >>> import polars as pl
+            >>> import pyarrow as pa
+            >>> data = {
+            ...     "a": [1.0, 2],
+            ...     "b": [3.0, float("inf")],
+            ... }
+
+            We define a library agnostic function:
+
+            >>> @nw.narwhalify
+            ... def func(df):
+            ...     return df.select(nw.all().is_finite())
+
+            We can then pass any supported library such as Pandas, Polars, or PyArrow to `func`:
+
+            >>> func(pd.DataFrame(data))
+                  a      b
+            0  True   True
+            1  True  False
+
+            >>> func(pl.DataFrame(data))
+            shape: (2, 2)
+            ┌──────┬───────┐
+            │ a    ┆ b     │
+            │ ---  ┆ ---   │
+            │ bool ┆ bool  │
+            ╞══════╪═══════╡
+            │ true ┆ true  │
+            │ true ┆ false │
+            └──────┴───────┘
+
+            >>> func(pa.table(data))
+            pyarrow.Table
+            a: bool
+            b: bool
+            ----
+            a: [[true,true]]
+            b: [[true,false]]
+        """
+        return self.__class__(lambda plx: self._call(plx).is_finite())
+
     @property
     def str(self: Self) -> ExprStringNamespace[Self]:
         return ExprStringNamespace(self)

narwhals/series.py

@@ -2525,6 +2525,52 @@ def mode(self: Self) -> Self:
         """
         return self._from_compliant_series(self._compliant_series.mode())
 
+    def is_finite(self: Self) -> Self:
+        """
+        Returns a boolean Series indicating which values are finite.
+
+        Returns:
+            Expression of `Boolean` data type.
+
+        Examples:
+            >>> import narwhals as nw
+            >>> import pandas as pd
+            >>> import polars as pl
+            >>> import pyarrow as pa
+            >>> data = [1.0, float("inf")]
+
+            We define a library agnostic function:
+
+            >>> @nw.narwhalify
+            ... def func(s):
+            ...     return s.is_finite()
+
+            We can then pass any supported library such as Pandas, Polars, or PyArrow to `func`:
+
+            >>> func(pd.Series(data))
+            0     True
+            1    False
+            dtype: bool
+
+            >>> func(pl.Series(data))  # doctest: +NORMALIZE_WHITESPACE
+            shape: (2,)
+            Series: '' [bool]
+            [
+               true
+               false
+            ]
+
+            >>> func(pa.chunked_array([data]))  # doctest: +ELLIPSIS
+            <pyarrow.lib.ChunkedArray object at ...>
+            [
+              [
+                true,
+                false
+              ]
+            ]
+        """
+        return self._from_compliant_series(self._compliant_series.is_finite())
+
     def __iter__(self: Self) -> Iterator[Any]:
         yield from self._compliant_series.__iter__()