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Try casting structs by name before by position #6726

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Try casting structs by name before by position #6726

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163 changes: 157 additions & 6 deletions arrow-cast/src/cast/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -187,12 +187,32 @@ pub fn can_cast_types(from_type: &DataType, to_type: &DataType) -> bool {
// Utf8 to decimal
(Utf8 | LargeUtf8, Decimal128(_, _) | Decimal256(_, _)) => true,
(Struct(from_fields), Struct(to_fields)) => {
from_fields.len() == to_fields.len() &&
from_fields.iter().zip(to_fields.iter()).all(|(f1, f2)| {
// Assume that nullability between two structs are compatible, if not,
// cast kernel will return error.
can_cast_types(f1.data_type(), f2.data_type())
})
if from_fields.len() != to_fields.len() {
return false;
}

// first, try casting each field by field name
let can_cast_by_name = to_fields.iter().all(|to_field| {
from_fields.iter()
.find(|from_field| from_field.name() == to_field.name())
.map_or(false, |from_field| {
// Assume that nullability between two structs are compatible.
can_cast_types(from_field.data_type(), to_field.data_type())
})
});

if can_cast_by_name {
return true;
}

// if the cast is not possible by field name, try by field position
let can_cast_by_position = from_fields.iter().zip(to_fields.iter()).all(|(f1, f2)| {
// Assume that nullability between two structs are compatible, if not,
// cast kernel will return error.
can_cast_types(f1.data_type(), f2.data_type())
});

can_cast_by_position
}
(Struct(_), _) => false,
(_, Struct(_)) => false,
Expand Down Expand Up @@ -1170,6 +1190,26 @@ pub fn cast_with_options(
}
(Struct(_), Struct(to_fields)) => {
let array = array.as_struct();

// first, try casting fields by name
let fields = to_fields
.iter()
.map(|field| {
array.column_by_name(field.name()).and_then(|array| {
cast_with_options(array.as_ref(), field.data_type(), cast_options).ok()
})
})
.collect::<Option<Vec<ArrayRef>>>();

if let Some(fields) = fields {
return Ok(Arc::new(StructArray::try_new(
to_fields.clone(),
fields,
array.nulls().cloned(),
)?) as ArrayRef);
}

// if fields by name failed, try casting fields by position
let fields = array
.columns()
.iter()
Expand Down Expand Up @@ -9721,6 +9761,117 @@ mod tests {
);
}

#[test]
fn test_cast_struct_to_struct_by_name() {
let from_type = DataType::Struct(
vec![
Field::new("a", DataType::Int32, true),
Field::new("b", DataType::Int32, true),
]
.into(),
);

let to_type = DataType::Struct(
vec![
Field::new("b", DataType::Int64, true),
Field::new("a", DataType::Int64, true),
]
.into(),
);

assert!(can_cast_types(&from_type, &to_type));

let array = StructArray::from(vec![
(
Arc::new(Field::new("a", DataType::Int32, true)),
Arc::new(Int32Array::from(vec![1, 2, 3, 4])) as ArrayRef,
),
(
Arc::new(Field::new("b", DataType::Int32, true)),
Arc::new(Int32Array::from(vec![5, 6, 7, 8])) as ArrayRef,
),
]);

let casted_array = cast(&array, &to_type).unwrap();

let casted_array = casted_array.as_struct();

assert_eq!(casted_array.data_type(), &to_type);

let casted_a = casted_array
.column_by_name("a")
.unwrap()
.as_any()
.downcast_ref::<Int64Array>()
.unwrap();
let casted_b = casted_array
.column_by_name("b")
.unwrap()
.as_any()
.downcast_ref::<Int64Array>()
.unwrap();

assert_eq!(casted_a.values(), &[1, 2, 3, 4]);

assert_eq!(casted_b.values(), &[5, 6, 7, 8]);
}

#[test]
fn test_cast_struct_to_struct_by_position() {
let from_type = DataType::Struct(
vec![
Field::new("b", DataType::Int32, true),
Field::new("a", DataType::Int32, true),
]
.into(),
);

let to_type = DataType::Struct(
vec![
Field::new("c", DataType::Int64, true),
Field::new("a", DataType::Int64, true),
]
.into(),
);

assert!(can_cast_types(&from_type, &to_type));

let array = StructArray::from(vec![
(
Arc::new(Field::new("b", DataType::Int32, true)),
Arc::new(Int32Array::from(vec![1, 2, 3, 4])) as ArrayRef,
),
(
Arc::new(Field::new("a", DataType::Int32, true)),
Arc::new(Int32Array::from(vec![5, 6, 7, 8])) as ArrayRef,
),
]);

let casted_array = cast(&array, &to_type).unwrap();

let casted_array = casted_array.as_struct();

assert_eq!(casted_array.data_type(), &to_type);

let casted_c = casted_array
.column_by_name("c")
.unwrap()
.as_any()
.downcast_ref::<Int64Array>()
.unwrap();

let casted_a = casted_array
.column_by_name("a")
.unwrap()
.as_any()
.downcast_ref::<Int64Array>()
.unwrap();

assert_eq!(casted_c.values(), &[1, 2, 3, 4]);

assert_eq!(casted_a.values(), &[5, 6, 7, 8]);
}

#[test]
fn test_cast_struct_to_struct_nullability() {
let boolean = Arc::new(BooleanArray::from(vec![false, false, true, true]));
Expand Down
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