sdf-jkl commented on code in PR #10313:
URL: https://github.com/apache/arrow-rs/pull/10313#discussion_r3731616433
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parquet-variant-compute/src/variant_to_arrow.rs:
##########
@@ -661,6 +674,216 @@ impl<'a> StructVariantToArrowRowBuilder<'a> {
}
}
+/// Builder for converting variant values into a [`UnionArray`].
+///
+/// Each value is dispatched to the union field that most exactly represents
its runtime type
+/// (see [`union_child_rank`]), with ties broken by declaration order. Unions
have no top-level
+/// null buffer, so null rows -- and, in safe mode, values no field can
represent -- become a
+/// null in the [`DataType::Null`] child if the union declares one, otherwise
in the first child.
+pub(crate) struct UnionVariantToArrowRowBuilder<'a> {
+ fields: &'a UnionFields,
+ mode: UnionMode,
+ children: Vec<UnionChildBuilder<'a>>,
+ type_ids: Vec<i8>,
+ /// Dense mode only
+ offsets: Vec<i32>,
+ null_child: usize,
+ cast_options: &'a CastOptions<'a>,
+}
+
+struct UnionChildBuilder<'a> {
+ type_id: i8,
+ builder: VariantToArrowRowBuilder<'a>,
+ len: i32,
+}
+
+impl<'a> UnionVariantToArrowRowBuilder<'a> {
+ fn try_new(
+ fields: &'a UnionFields,
+ mode: UnionMode,
+ cast_options: &'a CastOptions<'a>,
+ capacity: usize,
+ ) -> Result<Self> {
+ // null rows need a child to land in
+ if fields.is_empty() {
+ return Err(ArrowError::InvalidArgumentError(
+ "Casting Variant to a union requires at least one union
field".to_string(),
+ ));
+ }
+ let mut children = Vec::with_capacity(fields.len());
+ for (type_id, field) in fields.iter() {
+ children.push(UnionChildBuilder {
+ type_id,
+ builder: make_typed_variant_to_arrow_row_builder(
+ field.data_type(),
+ cast_options,
+ capacity,
+ )?,
+ len: 0,
+ });
+ }
+ let null_child = fields
+ .iter()
+ .position(|(_, field)| field.data_type() == &DataType::Null)
+ .unwrap_or(0);
+ let offsets = match mode {
+ UnionMode::Dense => Vec::with_capacity(capacity),
+ UnionMode::Sparse => Vec::new(),
+ };
+ Ok(Self {
+ fields,
+ mode,
+ children,
+ type_ids: Vec::with_capacity(capacity),
+ offsets,
+ null_child,
+ cast_options,
+ })
+ }
+
+ fn append_null(&mut self) -> Result<()> {
+ self.append_to_child(self.null_child, None)?;
+ Ok(())
+ }
+
+ fn append_value(&mut self, value: &Variant<'_, '_>) -> Result<bool> {
+ // `Variant::Null` becomes null even in strict mode, like in the other
builders
+ if matches!(value, Variant::Null) {
+ self.append_null()?;
+ return Ok(false);
+ }
+ match self.select_child(value) {
+ Some(index) => self.append_to_child(index, Some(value)),
+ None if self.cast_options.safe => {
+ self.append_null()?;
+ Ok(false)
+ }
+ None => Err(ArrowError::CastError(format!(
+ "Failed to cast variant {value:?} to union: no field can
represent it"
+ ))),
+ }
+ }
+
+ fn select_child(&self, value: &Variant<'_, '_>) -> Option<usize> {
+ let mut best: Option<(u8, usize)> = None;
+ for (index, (_, field)) in self.fields.iter().enumerate() {
+ let Some(rank) = union_child_rank(value, field.data_type()) else {
+ continue;
+ };
+ if best.is_none_or(|(best_rank, _)| rank < best_rank) {
+ best = Some((rank, index));
+ }
+ }
+ best.map(|(_, index)| index)
+ }
+
+ fn append_to_child(&mut self, index: usize, value: Option<&Variant<'_,
'_>>) -> Result<bool> {
+ self.type_ids.push(self.children[index].type_id);
+ match self.mode {
+ UnionMode::Dense => {
+ let child = &mut self.children[index];
+ self.offsets.push(child.len);
+ child.len = child.len.add_checked(1)?;
+ match value {
+ Some(value) => child.builder.append_value(value.clone()),
+ None => {
+ child.builder.append_null()?;
+ Ok(false)
+ }
+ }
+ }
+ UnionMode::Sparse => {
+ let mut appended = false;
+ for (child_index, child) in
self.children.iter_mut().enumerate() {
+ match value {
+ Some(value) if child_index == index => {
+ appended =
child.builder.append_value(value.clone())?;
+ }
+ _ => child.builder.append_null()?,
+ }
+ }
+ Ok(appended)
+ }
+ }
+ }
+
+ fn finish(self) -> Result<ArrayRef> {
+ let mut type_ids = Vec::with_capacity(self.children.len());
+ let mut fields = Vec::with_capacity(self.children.len());
+ let mut arrays = Vec::with_capacity(self.children.len());
+ for (child, (_, field)) in
self.children.into_iter().zip(self.fields.iter()) {
+ let array = child.builder.finish()?;
+ type_ids.push(child.type_id);
+ fields.push(
+ field
+ .as_ref()
+ .clone()
+ .with_data_type(array.data_type().clone()),
+ );
+ arrays.push(array);
+ }
+ let fields = UnionFields::try_new(type_ids, fields)?;
+ let offsets = (self.mode == UnionMode::Dense).then(||
ScalarBuffer::from(self.offsets));
+ let array =
+ UnionArray::try_new(fields, ScalarBuffer::from(self.type_ids),
offsets, arrays)?;
+ Ok(Arc::new(array))
+ }
+}
+
+/// Ranks how exactly a union child of type `data_type` can represent a
variant value's runtime
+/// type: 0 is the value's natural Arrow type, higher ranks are lossless
widenings, and `None`
+/// means the child cannot represent the value losslessly. Every pair admitted
here must be
+/// convertible by the corresponding row builder.
+fn union_child_rank(value: &Variant<'_, '_>, data_type: &DataType) ->
Option<u8> {
+ use DataType::*;
+ let rank = match (value, data_type) {
+ (Variant::BooleanTrue | Variant::BooleanFalse, Boolean) => 0,
+ (Variant::Int8(_), Int8) => 0,
+ (Variant::Int8(_), Int16) => 1,
+ (Variant::Int8(_), Int32) => 2,
+ (Variant::Int8(_), Int64) => 3,
+ (Variant::Int16(_), Int16) => 0,
+ (Variant::Int16(_), Int32) => 1,
+ (Variant::Int16(_), Int64) => 2,
+ (Variant::Int32(_), Int32) => 0,
+ (Variant::Int32(_), Int64) => 1,
+ (Variant::Int64(_), Int64) => 0,
+ (Variant::Float(_), Float32) => 0,
+ (Variant::Float(_), Float64) => 1,
+ (Variant::Double(_), Float64) => 0,
+ (Variant::Decimal4(_), Decimal32(..)) => 0,
+ (Variant::Decimal4(_), Decimal64(..)) => 1,
+ (Variant::Decimal4(_), Decimal128(..)) => 2,
+ (Variant::Decimal4(_), Decimal256(..)) => 3,
+ (Variant::Decimal8(_), Decimal64(..)) => 0,
+ (Variant::Decimal8(_), Decimal128(..)) => 1,
+ (Variant::Decimal8(_), Decimal256(..)) => 2,
+ (Variant::Decimal16(_), Decimal128(..)) => 0,
+ (Variant::Decimal16(_), Decimal256(..)) => 1,
+ (Variant::Date(_), Date32) => 0,
+ (Variant::Date(_), Date64) => 1,
+ (Variant::TimestampMicros(_), Timestamp(TimeUnit::Microsecond,
Some(_))) => 0,
+ (Variant::TimestampMicros(_), Timestamp(TimeUnit::Nanosecond,
Some(_))) => 1,
+ (Variant::TimestampNanos(_), Timestamp(TimeUnit::Nanosecond, Some(_)))
=> 0,
+ (Variant::TimestampNtzMicros(_), Timestamp(TimeUnit::Microsecond,
None)) => 0,
+ (Variant::TimestampNtzMicros(_), Timestamp(TimeUnit::Nanosecond,
None)) => 1,
+ (Variant::TimestampNtzNanos(_), Timestamp(TimeUnit::Nanosecond, None))
=> 0,
+ (Variant::Time(_), Time64(TimeUnit::Microsecond)) => 0,
+ (Variant::Time(_), Time64(TimeUnit::Nanosecond)) => 1,
+ (Variant::String(_) | Variant::ShortString(_), Utf8 | LargeUtf8 |
Utf8View) => 0,
+ (Variant::Binary(_), Binary | LargeBinary | BinaryView) => 0,
+ (Variant::Uuid(_), FixedSizeBinary(16)) => 0,
+ (Variant::Object(_), Struct(_)) => 0,
Review Comment:
same here -
https://github.com/apache/arrow-rs/pull/10313/commits/4bac07b29b6e9aa9968623ac3436430bedf335cc
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