brancz opened a new issue, #8870:
URL: https://github.com/apache/arrow-rs/issues/8870
**Describe the bug**
Casting struct arrays requires fields to be in the same order in the source
as the cast requests. Struct field order is intended to be irrelevant though.
**To Reproduce**
```
#[test]
fn test_cast_struct_with_different_field_order() {
// Test slow path: fields are in different order
let boolean = Arc::new(BooleanArray::from(vec![false, false, true,
true]));
let int = Arc::new(Int32Array::from(vec![42, 28, 19, 31]));
let string = Arc::new(StringArray::from(vec!["foo", "bar", "baz",
"qux"]));
let struct_array = StructArray::from(vec![
(
Arc::new(Field::new("a", DataType::Boolean, false)),
boolean.clone() as ArrayRef,
),
(
Arc::new(Field::new("b", DataType::Int32, false)),
int.clone() as ArrayRef,
),
(
Arc::new(Field::new("c", DataType::Utf8, false)),
string.clone() as ArrayRef,
),
]);
// Target has fields in different order: c, a, b instead of a, b, c
let to_type = DataType::Struct(
vec![
Field::new("c", DataType::Utf8, false),
Field::new("a", DataType::Utf8, false), // Boolean to Utf8
Field::new("b", DataType::Utf8, false), // Int32 to Utf8
]
.into(),
);
let result = cast(&struct_array, &to_type).unwrap();
let result_struct = result.as_struct();
assert_eq!(result_struct.data_type(), &to_type);
assert_eq!(result_struct.num_columns(), 3);
// Verify field "c" (originally position 2, now position 0) remains
Utf8
let c_column = result_struct.column(0).as_string::<i32>();
assert_eq!(
c_column.into_iter().flatten().collect::<Vec<_>>(),
vec!["foo", "bar", "baz", "qux"]
);
// Verify field "a" (originally position 0, now position 1) was cast
from Boolean to Utf8
let a_column = result_struct.column(1).as_string::<i32>();
assert_eq!(
a_column.into_iter().flatten().collect::<Vec<_>>(),
vec!["false", "false", "true", "true"]
);
// Verify field "b" (originally position 1, now position 2) was cast
from Int32 to Utf8
let b_column = result_struct.column(2).as_string::<i32>();
assert_eq!(
b_column.into_iter().flatten().collect::<Vec<_>>(),
vec!["42", "28", "19", "31"]
);
}
```
**Expected behavior**
The above works, and casting should happen field-wise.
**Additional context**
I already have a patch, but opening this for tracking purposes.
@alamb @vegarsti
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