add native union type casting support#9544
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friendlymatthew wants to merge 1 commit intoapache:mainfrom
Open
add native union type casting support#9544friendlymatthew wants to merge 1 commit intoapache:mainfrom
friendlymatthew wants to merge 1 commit intoapache:mainfrom
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friendlymatthew
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Mar 12, 2026
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self review
arrow-cast/src/cast/mod.rs
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| (_, Union(_, _)) => Err(ArrowError::CastError(format!( | ||
| "Casting from {from_type} to {to_type} not supported" | ||
| ))), |
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This PR does not support casting scalar types into a Union type
It's not a feature that we currently need and will probably need more complex work to get it correct. Though, I think this is a cool/valid feature. I can file an issue if liked
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| let type_ids = array.type_ids().clone(); | ||
| let offsets = array.offsets().cloned(); | ||
|
|
||
| let new_children: Vec<ArrayRef> = from_fields | ||
| .iter() | ||
| .map(|(from_id, _from_field)| { | ||
| let (_, to_field) = to_fields | ||
| .iter() | ||
| .find(|(to_id, _)| *to_id == from_id) | ||
| .ok_or_else(|| { | ||
| ArrowError::CastError(format!( | ||
| "Cannot cast union: type_id {from_id} not found in target union" | ||
| )) | ||
| })?; | ||
| let child = array.child(from_id); | ||
| cast_with_options(child.as_ref(), to_field.data_type(), cast_options) | ||
| }) | ||
| .collect::<Result<_, _>>()?; |
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look ups like this can go from n^2 to nlogn if we implement #8937, since sorting by type_id will give us logn searching
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Which issue does this PR close?
arrow-cast#9225Rationale for this change
This PR adds native support for casting Union arrays in the cast kernel. Previously,
can_cast_typesandcast_with_optionshad no handling for union types at all