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Avoid a clone when creating MapArray from ArrayData #9192

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Merged
Dandandan merged 2 commits into from
Jan 18, 2026
Merged

Avoid a clone when creating MapArray from ArrayData #9192

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Avoid a clone when creating `MapArray` from ArrayData
alamb Jan 15, 2026
459441b
Merge branch 'main' into alamb/map_array
alamb Jan 16, 2026
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27 changes: 14 additions & 13 deletions arrow-array/src/array/map_array.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@
// specific language governing permissions and limitations
// under the License.

use crate::array::{get_offsets, print_long_array};
use crate::array::{get_offsets_from_buffer, print_long_array};
use crate::iterator::MapArrayIter;
use crate::{Array, ArrayAccessor, ArrayRef, ListArray, StringArray, StructArray, make_array};
use arrow_buffer::{ArrowNativeType, Buffer, NullBuffer, OffsetBuffer, ToByteSlice};
Expand Down Expand Up @@ -272,28 +272,29 @@ impl From<MapArray> for ArrayData {

impl MapArray {
fn try_new_from_array_data(data: ArrayData) -> Result<Self, ArrowError> {
if !matches!(data.data_type(), DataType::Map(_, _)) {
let (data_type, len, nulls, offset, mut buffers, mut child_data) = data.into_parts();

if !matches!(data_type, DataType::Map(_, _)) {
return Err(ArrowError::InvalidArgumentError(format!(
"MapArray expected ArrayData with DataType::Map got {}",
data.data_type()
"MapArray expected ArrayData with DataType::Map got {data_type}",
)));
}

if data.buffers().len() != 1 {
if buffers.len() != 1 {
return Err(ArrowError::InvalidArgumentError(format!(
"MapArray data should contain a single buffer only (value offsets), had {}",
data.len()
buffers.len(),
)));
}
let buffer = buffers.pop().expect("checked above");

if data.child_data().len() != 1 {
if child_data.len() != 1 {
return Err(ArrowError::InvalidArgumentError(format!(
"MapArray should contain a single child array (values array), had {}",
data.child_data().len()
child_data.len()
)));
}

let entries = data.child_data()[0].clone();
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Contributor Author

@alamb alamb Jan 15, 2026 •
edited
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Here is a clone of ArrayData that is avoided

let entries = child_data.pop().expect("checked above");

if let DataType::Struct(fields) = entries.data_type() {
if fields.len() != 2 {
Expand All @@ -312,11 +313,11 @@ impl MapArray {

// SAFETY:
// ArrayData is valid, and verified type above
let value_offsets = unsafe { get_offsets(&data) };
let value_offsets = unsafe { get_offsets_from_buffer(buffer, offset, len) };

Ok(Self {
data_type: data.data_type().clone(),
nulls: data.nulls().cloned(),
data_type,
nulls,
entries,
value_offsets,
})
Expand Down
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