Dandandan commented on a change in pull request #1248:
URL: https://github.com/apache/arrow-rs/pull/1248#discussion_r800150479
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File path: arrow/src/compute/kernels/filter.rs
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@@ -185,79 +287,585 @@ pub fn prep_null_mask_filter(filter: &BooleanArray) ->
BooleanArray {
/// # Ok(())
/// # }
/// ```
-pub fn filter(array: &dyn Array, predicate: &BooleanArray) -> Result<ArrayRef>
{
- if predicate.null_count() > 0 {
- // this greatly simplifies subsequent filtering code
- // now we only have a boolean mask to deal with
- let predicate = prep_null_mask_filter(predicate);
- return filter(array, &predicate);
+pub fn filter(values: &dyn Array, predicate: &BooleanArray) ->
Result<ArrayRef> {
+ let predicate = FilterBuilder::new(predicate).build();
+ filter_array(values, &predicate)
+}
+
+/// Returns a new [RecordBatch] with arrays containing only values matching
the filter.
+pub fn filter_record_batch(
+ record_batch: &RecordBatch,
+ predicate: &BooleanArray,
+) -> Result<RecordBatch> {
+ let mut filter_builder = FilterBuilder::new(predicate);
+ if record_batch.num_columns() > 1 {
+ // Only optimize if filtering more than one column
+ filter_builder = filter_builder.optimize();
+ }
+ let filter = filter_builder.build();
+
+ let filtered_arrays = record_batch
+ .columns()
+ .iter()
+ .map(|a| filter_array(a, &filter))
+ .collect::<Result<Vec<_>>>()?;
+
+ RecordBatch::try_new(record_batch.schema(), filtered_arrays)
+}
+
+/// A builder to construct [`FilterPredicate`]
+#[derive(Debug)]
+pub struct FilterBuilder {
+ filter: BooleanArray,
+ count: usize,
+ strategy: IterationStrategy,
+}
+
+impl FilterBuilder {
+ /// Create a new [`FilterBuilder`] that can be used to construct a
[`FilterPredicate`]
+ pub fn new(filter: &BooleanArray) -> Self {
+ let filter = match filter.null_count() {
+ 0 => BooleanArray::from(filter.data().clone()),
+ _ => prep_null_mask_filter(filter),
+ };
+
+ let count = filter_count(&filter);
+ // Compute the selectivity of the predicate by dividing the number of
true
+ // bits in the predicate by the predicate's total length
+ //
+ // This can then be used as a heuristic for the optimal iteration
strategy
+ let selectivity_frac = count as f64 / filter.len() as f64;
+ let strategy = if selectivity_frac >
FILTER_SLICES_SELECTIVITY_THRESHOLD {
+ IterationStrategy::SlicesIterator
+ } else {
+ IterationStrategy::IndexIterator
+ };
+
+ Self {
+ filter,
+ count,
+ strategy,
+ }
}
- let filter_count = filter_count(predicate);
+ /// Compute an optimised representation of the provided `filter` mask that
can be
+ /// applied to an array more quickly.
+ ///
+ /// Note: There is limited benefit to calling this to then filter a single
array
+ /// Note: This will likely have a larger memory footprint than the
original mask
+ pub fn optimize(mut self) -> Self {
+ match self.strategy {
+ IterationStrategy::SlicesIterator => {
+ let slices = SlicesIterator::new(&self.filter).collect();
+ self.strategy = IterationStrategy::Slices(slices)
+ }
+ IterationStrategy::IndexIterator => {
+ let indices = IndexIterator::new(&self.filter,
self.count).collect();
+ self.strategy = IterationStrategy::Indices(indices)
+ }
+ _ => {}
+ }
+ self
+ }
- match filter_count {
+ /// Construct the final `FilterPredicate`
+ pub fn build(self) -> FilterPredicate {
+ FilterPredicate {
+ filter: self.filter,
+ count: self.count,
+ strategy: self.strategy,
+ }
+ }
+}
+
+/// The iteration strategy used to evaluate [`FilterPredicate`]
+#[derive(Debug)]
+enum IterationStrategy {
+ // A lazily evaluated iterator of ranges
+ SlicesIterator,
+ // A lazily evaluated iterator of indices
+ IndexIterator,
+ // A precomputed list of indices
+ Indices(Vec<usize>),
+ // A precomputed array of ranges
+ Slices(Vec<(usize, usize)>),
+}
+
+/// A filtering predicate that can be applied to an [`Array`]
+#[derive(Debug)]
+pub struct FilterPredicate {
+ filter: BooleanArray,
+ count: usize,
+ strategy: IterationStrategy,
+}
+
+impl FilterPredicate {
+ /// Selects rows from `values` based on this [`FilterPredicate`]
+ pub fn filter(&self, values: &dyn Array) -> Result<ArrayRef> {
+ filter_array(values, self)
+ }
+}
+
+fn filter_array(values: &dyn Array, predicate: &FilterPredicate) ->
Result<ArrayRef> {
+ if predicate.filter.len() > values.len() {
+ return Err(ArrowError::InvalidArgumentError(format!(
+ "Filter predicate of length {} is larger than target array of
length {}",
+ predicate.filter.len(),
+ values.len()
+ )));
+ }
+
+ match predicate.count {
0 => {
// return empty
- Ok(new_empty_array(array.data_type()))
+ Ok(new_empty_array(values.data_type()))
}
- len if len == array.len() => {
+ len if len == values.len() => {
// return all
- let data = array.data().clone();
+ let data = values.data().clone();
Ok(make_array(data))
}
- _ => {
- // actually filter
- let mut mutable =
- MutableArrayData::new(vec![array.data_ref()], false,
filter_count);
+ // actually filter
+ _ => match values.data_type() {
+ DataType::Boolean => {
+ let values =
values.as_any().downcast_ref::<BooleanArray>().unwrap();
+ Ok(Arc::new(filter_boolean(values, predicate)))
+ }
+ DataType::Int8 => {
+ downcast_filter!(Int8Type, values, predicate)
+ }
+ DataType::Int16 => {
+ downcast_filter!(Int16Type, values, predicate)
+ }
+ DataType::Int32 => {
+ downcast_filter!(Int32Type, values, predicate)
+ }
+ DataType::Int64 => {
+ downcast_filter!(Int64Type, values, predicate)
+ }
+ DataType::UInt8 => {
+ downcast_filter!(UInt8Type, values, predicate)
+ }
+ DataType::UInt16 => {
+ downcast_filter!(UInt16Type, values, predicate)
+ }
+ DataType::UInt32 => {
+ downcast_filter!(UInt32Type, values, predicate)
+ }
+ DataType::UInt64 => {
+ downcast_filter!(UInt64Type, values, predicate)
+ }
+ DataType::Float32 => {
+ downcast_filter!(Float32Type, values, predicate)
+ }
+ DataType::Float64 => {
+ downcast_filter!(Float64Type, values, predicate)
+ }
+ DataType::Date32 => {
+ downcast_filter!(Date32Type, values, predicate)
+ }
+ DataType::Date64 => {
+ downcast_filter!(Date64Type, values, predicate)
+ }
+ DataType::Time32(Second) => {
+ downcast_filter!(Time32SecondType, values, predicate)
+ }
+ DataType::Time32(Millisecond) => {
+ downcast_filter!(Time32MillisecondType, values, predicate)
+ }
+ DataType::Time64(Microsecond) => {
+ downcast_filter!(Time64MicrosecondType, values, predicate)
+ }
+ DataType::Time64(Nanosecond) => {
+ downcast_filter!(Time64NanosecondType, values, predicate)
+ }
+ DataType::Timestamp(Second, _) => {
+ downcast_filter!(TimestampSecondType, values, predicate)
+ }
+ DataType::Timestamp(Millisecond, _) => {
+ downcast_filter!(TimestampMillisecondType, values, predicate)
+ }
+ DataType::Timestamp(Microsecond, _) => {
+ downcast_filter!(TimestampMicrosecondType, values, predicate)
+ }
+ DataType::Timestamp(Nanosecond, _) => {
+ downcast_filter!(TimestampNanosecondType, values, predicate)
+ }
+ DataType::Interval(IntervalUnit::YearMonth) => {
+ downcast_filter!(IntervalYearMonthType, values, predicate)
+ }
+ DataType::Interval(IntervalUnit::DayTime) => {
+ downcast_filter!(IntervalDayTimeType, values, predicate)
+ }
+ DataType::Interval(IntervalUnit::MonthDayNano) => {
+ downcast_filter!(IntervalMonthDayNanoType, values, predicate)
+ }
+ DataType::Duration(TimeUnit::Second) => {
+ downcast_filter!(DurationSecondType, values, predicate)
+ }
+ DataType::Duration(TimeUnit::Millisecond) => {
+ downcast_filter!(DurationMillisecondType, values, predicate)
+ }
+ DataType::Duration(TimeUnit::Microsecond) => {
+ downcast_filter!(DurationMicrosecondType, values, predicate)
+ }
+ DataType::Duration(TimeUnit::Nanosecond) => {
+ downcast_filter!(DurationNanosecondType, values, predicate)
+ }
+ DataType::Utf8 => {
+ let values = values
+ .as_any()
+ .downcast_ref::<GenericStringArray<i32>>()
+ .unwrap();
+ Ok(Arc::new(filter_string::<i32>(values, predicate)))
+ }
+ DataType::LargeUtf8 => {
+ let values = values
+ .as_any()
+ .downcast_ref::<GenericStringArray<i64>>()
+ .unwrap();
+ Ok(Arc::new(filter_string::<i64>(values, predicate)))
+ }
+ DataType::Dictionary(key_type, _) => match key_type.as_ref() {
+ DataType::Int8 => downcast_dict_filter!(Int8Type, values,
predicate),
+ DataType::Int16 => downcast_dict_filter!(Int16Type, values,
predicate),
+ DataType::Int32 => downcast_dict_filter!(Int32Type, values,
predicate),
+ DataType::Int64 => downcast_dict_filter!(Int64Type, values,
predicate),
+ DataType::UInt8 => downcast_dict_filter!(UInt8Type, values,
predicate),
+ DataType::UInt16 => downcast_dict_filter!(UInt16Type, values,
predicate),
+ DataType::UInt32 => downcast_dict_filter!(UInt32Type, values,
predicate),
+ DataType::UInt64 => downcast_dict_filter!(UInt64Type, values,
predicate),
+ t => {
+ unimplemented!("Filter not supported for dictionary key
type {:?}", t)
+ }
+ },
+ _ => {
+ // fallback to using MutableArrayData
+ let mut mutable = MutableArrayData::new(
+ vec![values.data_ref()],
+ false,
+ predicate.count,
+ );
+
+ match &predicate.strategy {
+ IterationStrategy::Slices(slices) => {
+ slices
+ .iter()
+ .for_each(|(start, end)| mutable.extend(0, *start,
*end));
+ }
+ _ => {
+ let iter = SlicesIterator::new(&predicate.filter);
+ iter.for_each(|(start, end)| mutable.extend(0, start,
end));
+ }
+ }
+
+ let data = mutable.freeze();
+ Ok(make_array(data))
+ }
+ },
+ }
+}
+
+/// Computes a new null mask for `data` based on `predicate`
+///
+/// If the predicate selected no null-rows, returns `None`, otherwise returns
+/// `Some((null_count, null_buffer))` where `null_count` is the number of nulls
+/// in the filtered output, and `null_buffer` is the filtered null buffer
+///
+fn filter_null_mask(
+ data: &ArrayData,
+ predicate: &FilterPredicate,
+) -> Option<(usize, Buffer)> {
+ if data.null_count() == 0 {
+ return None;
+ }
+
+ let nulls = filter_bits(data.null_buffer()?, data.offset(), predicate);
+ // The filtered `nulls` has a length of `predicate.count` bits and
+ // therefore the null count is this minus the number of valid bits
+ let null_count = predicate.count - nulls.count_set_bits();
+
+ if null_count == 0 {
+ return None;
+ }
+
+ Some((null_count, nulls))
+}
+
+/// Filter the packed bitmask `buffer`, with `predicate` starting at bit
offset `offset`
+fn filter_bits(buffer: &Buffer, offset: usize, predicate: &FilterPredicate) ->
Buffer {
+ let src = buffer.as_slice();
+
+ match &predicate.strategy {
+ IterationStrategy::IndexIterator => {
+ let bits = IndexIterator::new(&predicate.filter, predicate.count)
+ .map(|src_idx| bit_util::get_bit(src, src_idx + offset));
+
+ // SAFETY: `IndexIterator` reports its size correctly
+ unsafe { MutableBuffer::from_trusted_len_iter_bool(bits).into() }
+ }
+ IterationStrategy::Indices(indices) => {
+ let bits = indices
+ .iter()
+ .map(|src_idx| bit_util::get_bit(src, *src_idx + offset));
- let iter = SlicesIterator::new(predicate);
- iter.for_each(|(start, end)| mutable.extend(0, start, end));
+ // SAFETY: `Vec::iter()` reports its size correctly
+ unsafe { MutableBuffer::from_trusted_len_iter_bool(bits).into() }
+ }
+ IterationStrategy::SlicesIterator => {
+ let mut builder =
+ BooleanBufferBuilder::new(bit_util::ceil(predicate.count, 8));
+ for (start, end) in SlicesIterator::new(&predicate.filter) {
+ builder.append_packed_range(start + offset..end + offset, src)
+ }
+ builder.finish()
+ }
+ IterationStrategy::Slices(slices) => {
+ let mut builder =
+ BooleanBufferBuilder::new(bit_util::ceil(predicate.count, 8));
+ for (start, end) in slices {
+ builder.append_packed_range(*start + offset..*end + offset,
src)
+ }
+ builder.finish()
+ }
+ }
+}
- let data = mutable.freeze();
- Ok(make_array(data))
+/// `filter` implementation for boolean buffers
+fn filter_boolean(values: &BooleanArray, predicate: &FilterPredicate) ->
BooleanArray {
+ let data = values.data();
+ assert_eq!(data.buffers().len(), 1);
+ assert_eq!(data.child_data().len(), 0);
+
+ let values = filter_bits(&data.buffers()[0], data.offset(), predicate);
+
+ let mut builder = ArrayDataBuilder::new(DataType::Boolean)
+ .len(predicate.count)
+ .add_buffer(values);
+
+ if let Some((null_count, nulls)) = filter_null_mask(data, predicate) {
+ builder = builder.null_count(null_count).null_bit_buffer(nulls);
+ }
+
+ let data = unsafe { builder.build_unchecked() };
+ BooleanArray::from(data)
+}
+
+/// `filter` implementation for primitive arrays
+fn filter_primitive<T>(
+ values: &PrimitiveArray<T>,
+ predicate: &FilterPredicate,
+) -> PrimitiveArray<T>
+where
+ T: ArrowPrimitiveType,
+{
+ let data = values.data();
+ assert_eq!(data.buffers().len(), 1);
+ assert_eq!(data.child_data().len(), 0);
+
+ let values = data.buffer::<T::Native>(0);
+ assert!(values.len() >= predicate.filter.len());
+
+ let buffer = match &predicate.strategy {
+ IterationStrategy::SlicesIterator => {
+ let mut buffer =
+ MutableBuffer::with_capacity(predicate.count *
T::get_byte_width());
+ for (start, end) in SlicesIterator::new(&predicate.filter) {
+ buffer.extend_from_slice(&values[start..end]);
+ }
+ buffer
+ }
+ IterationStrategy::Slices(slices) => {
+ let mut buffer =
+ MutableBuffer::with_capacity(predicate.count *
T::get_byte_width());
+ for (start, end) in slices {
+ buffer.extend_from_slice(&values[*start..*end]);
+ }
+ buffer
+ }
+ IterationStrategy::IndexIterator => {
+ let iter =
+ IndexIterator::new(&predicate.filter, predicate.count).map(|x|
values[x]);
+
+ // SAFETY: IndexIterator is trusted length
+ unsafe { MutableBuffer::from_trusted_len_iter(iter) }
}
+ IterationStrategy::Indices(indices) => {
+ let iter = indices.iter().map(|x| values[*x]);
+
+ // SAFETY: `Vec::iter` is trusted length
+ unsafe { MutableBuffer::from_trusted_len_iter(iter) }
+ }
+ };
+
+ let mut builder = ArrayDataBuilder::new(data.data_type().clone())
+ .len(predicate.count)
+ .add_buffer(buffer.into());
+
+ if let Some((null_count, nulls)) = filter_null_mask(data, predicate) {
+ builder = builder.null_count(null_count).null_bit_buffer(nulls);
}
+
+ let data = unsafe { builder.build_unchecked() };
+ PrimitiveArray::from(data)
}
-/// Returns a new [RecordBatch] with arrays containing only values matching
the filter.
-pub fn filter_record_batch(
- record_batch: &RecordBatch,
- predicate: &BooleanArray,
-) -> Result<RecordBatch> {
- if predicate.null_count() > 0 {
- // this greatly simplifies subsequent filtering code
- // now we only have a boolean mask to deal with
- let predicate = prep_null_mask_filter(predicate);
- return filter_record_batch(record_batch, &predicate);
+/// [`FilterString`] is created from a source [`GenericStringArray`] and can be
+/// used to build a new [`GenericStringArray`] by copying values from the
source
+///
+/// TODO(raphael): Could this be used for the take kernel as well?
+struct FilterString<'a, OffsetSize> {
+ src_offsets: &'a [OffsetSize],
+ src_values: &'a [u8],
+ dst_offsets: MutableBuffer,
+ dst_values: MutableBuffer,
+ cur_offset: OffsetSize,
+}
+
+impl<'a, OffsetSize> FilterString<'a, OffsetSize>
+where
+ OffsetSize: Zero + AddAssign + StringOffsetSizeTrait,
+{
+ fn new(capacity: usize, array: &'a GenericStringArray<OffsetSize>) -> Self
{
+ let num_offsets_bytes = (capacity + 1) *
std::mem::size_of::<OffsetSize>();
+ let mut dst_offsets = MutableBuffer::new(num_offsets_bytes);
+ let dst_values = MutableBuffer::new(0);
+ let cur_offset = OffsetSize::zero();
+ dst_offsets.push(cur_offset);
+
+ Self {
+ src_offsets: array.value_offsets(),
+ src_values: &array.data().buffers()[1],
+ dst_offsets,
+ dst_values,
+ cur_offset,
+ }
+ }
+
+ /// Returns the byte offset at `idx`
+ #[inline]
+ fn get_value_offset(&self, idx: usize) -> usize {
+ self.src_offsets[idx].to_usize().expect("illegal offset")
}
- let num_columns = record_batch.columns().len();
+ /// Returns the start and end of the value at index `idx` along with its
length
+ #[inline]
+ fn get_value_range(&self, idx: usize) -> (usize, usize, OffsetSize) {
+ // These can only fail if `array` contains invalid data
+ let start = self.get_value_offset(idx);
+ let end = self.get_value_offset(idx + 1);
+ let len = OffsetSize::from_usize(end - start).expect("illegal offset
range");
+ (start, end, len)
+ }
- let filtered_arrays = match num_columns {
- 1 => {
- vec![filter(record_batch.columns()[0].as_ref(), predicate)?]
+ /// Extends the in-progress array by the indexes in the provided iterator
+ fn extend_idx(&mut self, iter: impl Iterator<Item = usize>) {
+ for idx in iter {
+ let (start, end, len) = self.get_value_range(idx);
+ self.cur_offset += len;
+ self.dst_offsets.push(self.cur_offset);
+ self.dst_values
+ .extend_from_slice(&self.src_values[start..end]);
}
- _ => {
- let filter = build_filter(predicate)?;
- record_batch
- .columns()
- .iter()
- .map(|a| make_array(filter(a.data())))
- .collect()
+ }
+
+ /// Extends the in-progress array by the ranges in the provided iterator
+ fn extend_slices(&mut self, iter: impl Iterator<Item = (usize, usize)>) {
+ for slice in iter {
Review comment:
```suggestion
for (start, end) in iter {
```
Small style suggestion
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