fix[rust]: unset sorted flag on mutation (#4943)

polars/polars-core/src/chunked_array/arithmetic.rs

@@ -8,6 +8,7 @@ use arrow::compute::arity_assign;
 use num::{Num, NumCast, ToPrimitive};
 
 use crate::prelude::*;
+use crate::series::IsSorted;
 use crate::utils::{align_chunks_binary, align_chunks_binary_owned};
 
 macro_rules! apply_operand_on_chunkedarray_by_iter {
@@ -117,6 +118,7 @@ where
                     .zip(rhs.downcast_iter_mut())
                     .for_each(|(lhs, rhs)| kernel(lhs, rhs));
             }
+            lhs.set_sorted2(IsSorted::Not);
             lhs
         }
         // broadcast right path

polars/polars-core/src/chunked_array/ops/apply.rs

@@ -7,6 +7,7 @@ use polars_arrow::array::PolarsArray;
 use polars_arrow::trusted_len::PushUnchecked;
 
 use crate::prelude::*;
+use crate::series::IsSorted;
 use crate::utils::{CustomIterTools, NoNull};
 
 macro_rules! try_apply {
@@ -118,6 +119,8 @@ impl<T: PolarsNumericType> ChunkedArray<T> {
             self.downcast_iter_mut()
                 .for_each(|arr| arrow::compute::arity_assign::unary(arr, f))
         };
+        // can be in any order now
+        self.set_sorted2(IsSorted::Not);
     }
 }
 

polars/polars-core/src/chunked_array/ops/downcast.rs

@@ -55,7 +55,9 @@ where
     }
 
     /// # Safety
-    /// The caller must ensure the length remains correct.
+    /// The caller must ensure:
+    ///     * the length remains correct.
+    ///     * the flags (sorted, etc) are correct.
     pub unsafe fn downcast_iter_mut(
         &mut self,
     ) -> impl Iterator<Item = &mut PrimitiveArray<T::Native>> + DoubleEndedIterator {

polars/polars-ops/src/chunked_array/set.rs

@@ -1,6 +1,7 @@
 use polars_arrow::export::arrow::array::PrimitiveArray;
 use polars_core::export::arrow::array::Array;
 use polars_core::prelude::*;
+use polars_core::series::IsSorted;
 use polars_core::utils::arrow::bitmap::MutableBitmap;
 use polars_core::utils::arrow::types::NativeType;
 
@@ -127,6 +128,8 @@ where
 
         // safety:
         // we will not modify the length
+        // and we unset the sorted flag.
+        ca.set_sorted2(IsSorted::Not);
         let arr = unsafe { ca.downcast_iter_mut() }.next().unwrap();
         let len = arr.len();
 

py-polars/tests/unit/test_sort.py

@@ -233,3 +233,24 @@ def test_top_k() -> None:
 
     assert s.top_k(3).to_list() == [8, 5, 3]
     assert s.top_k(4, reverse=True).to_list() == [1, 2, 3, 5]
+
+
+def test_sorted_flag_unset_by_arithmetic_4937() -> None:
+    df = pl.DataFrame(
+        {
+            "ts": [1, 1, 1, 0, 1],
+            "price": [3.3, 3.0, 3.5, 3.6, 3.7],
+            "mask": [1, 1, 1, 1, 0],
+        }
+    )
+
+    assert df.sort("price").groupby("ts").agg(
+        [
+            (pl.col("price") * pl.col("mask")).max().alias("pmax"),
+            (pl.col("price") * pl.col("mask")).min().alias("pmin"),
+        ]
+    ).sort("ts").to_dict(False) == {
+        "ts": [0, 1],
+        "pmax": [3.6, 3.5],
+        "pmin": [3.6, 0.0],
+    }