fix: Include Array in to_physical (#19474)

Author: ritchie46

crates/polars-core/src/series/mod.rs

@@ -600,6 +600,7 @@ impl Series {
     /// * Time -> Int64
     /// * Categorical -> UInt32
     /// * List(inner) -> List(physical of inner)
+    /// * Array(inner) -> Array(physical of inner)
     /// * Struct -> Struct with physical repr of each struct column
     pub fn to_physical_repr(&self) -> Cow<Series> {
         use DataType::*;
@@ -620,6 +621,11 @@ impl Series {
                 Cow::Owned(ca.physical().clone().into_series())
             },
             List(inner) => Cow::Owned(self.cast(&List(Box::new(inner.to_physical()))).unwrap()),
+            #[cfg(feature = "dtype-array")]
+            Array(inner, size) => Cow::Owned(
+                self.cast(&Array(Box::new(inner.to_physical()), *size))
+                    .unwrap(),
+            ),
             #[cfg(feature = "dtype-struct")]
             Struct(_) => {
                 let arr = self.struct_().unwrap();

py-polars/polars/expr/expr.py

@@ -407,9 +407,16 @@ def to_physical(self) -> Expr:
         - :func:`polars.datatypes.Duration` -> :func:`polars.datatypes.Int64`
         - :func:`polars.datatypes.Categorical` -> :func:`polars.datatypes.UInt32`
         - `List(inner)` -> `List(physical of inner)`
+        - `Array(inner)` -> `Struct(physical of inner)`
+        - `Struct(fields)` -> `Array(physical of fields)`
 
         Other data types will be left unchanged.
 
+        Warning
+        -------
+        The physical representations are an implementation detail
+        and not guaranteed to be stable.
+
         Examples
         --------
         Replicating the pandas

py-polars/polars/series/series.py

@@ -4047,8 +4047,15 @@ def to_physical(self) -> Series:
         - :func:`polars.datatypes.Duration` -> :func:`polars.datatypes.Int64`
         - :func:`polars.datatypes.Categorical` -> :func:`polars.datatypes.UInt32`
         - `List(inner)` -> `List(physical of inner)`
+        - `Array(inner)` -> `Array(physical of inner)`
+        - `Struct(fields)` -> `Struct(physical of fields)`
         - Other data types will be left unchanged.
 
+        Warning
+        -------
+        The physical representations are an implementation detail
+        and not guaranteed to be stable.
+
         Examples
         --------
         Replicating the pandas