vortex_array/arrays/chunked/vtable/

canonical.rs

// SPDX-License-Identifier: Apache-2.0
// SPDX-FileCopyrightText: Copyright the Vortex contributors

use vortex_buffer::BufferMut;
use vortex_dtype::{DType, Nullability, PType, StructFields};
use vortex_error::VortexExpect;

use crate::arrays::{
    ChunkedArray, ChunkedVTable, ListViewArray, ListViewRebuildMode, PrimitiveArray, StructArray,
};
use crate::builders::{ArrayBuilder, builder_with_capacity};
use crate::compute::cast;
use crate::validity::Validity;
use crate::vtable::CanonicalVTable;
use crate::{Array, ArrayRef, Canonical, IntoArray, ToCanonical};

impl CanonicalVTable<ChunkedVTable> for ChunkedVTable {
    fn canonicalize(array: &ChunkedArray) -> Canonical {
        if array.nchunks() == 0 {
            return Canonical::empty(array.dtype());
        }
        if array.nchunks() == 1 {
            return array.chunks()[0].to_canonical();
        }

        match array.dtype() {
            DType::Struct(struct_dtype, _) => {
                let struct_array = pack_struct_chunks(
                    array.chunks(),
                    Validity::copy_from_array(array.as_ref()),
                    struct_dtype,
                );
                Canonical::Struct(struct_array)
            }
            DType::List(elem_dtype, _) => Canonical::List(swizzle_list_chunks(
                array.chunks(),
                Validity::copy_from_array(array.as_ref()),
                elem_dtype,
            )),
            _ => {
                let mut builder = builder_with_capacity(array.dtype(), array.len());
                array.append_to_builder(builder.as_mut());
                builder.finish_into_canonical()
            }
        }
    }

    fn append_to_builder(array: &ChunkedArray, builder: &mut dyn ArrayBuilder) {
        for chunk in array.chunks() {
            chunk.append_to_builder(builder);
        }
    }
}

/// Packs many [`StructArray`]s to instead be a single [`StructArray`], where the [`Array`] for each
/// field is a [`ChunkedArray`].
///
/// The caller guarantees there are at least 2 chunks.
fn pack_struct_chunks(
    chunks: &[ArrayRef],
    validity: Validity,
    struct_dtype: &StructFields,
) -> StructArray {
    let len = chunks.iter().map(|chunk| chunk.len()).sum();
    let mut field_arrays = Vec::new();

    for (field_idx, field_dtype) in struct_dtype.fields().enumerate() {
        let field_chunks = chunks
            .iter()
            .map(|c| {
                c.to_struct()
                    .fields()
                    .get(field_idx)
                    .vortex_expect("Invalid field index")
                    .to_array()
            })
            .collect::<Vec<_>>();

        // SAFETY: field_chunks are extracted from valid StructArrays with matching dtypes.
        // Each chunk's field array is guaranteed to be valid for field_dtype.
        let field_array = unsafe { ChunkedArray::new_unchecked(field_chunks, field_dtype.clone()) };
        field_arrays.push(field_array.into_array());
    }

    // SAFETY: field_arrays are built from corresponding chunks of same length, dtypes match by
    // construction.
    unsafe { StructArray::new_unchecked(field_arrays, struct_dtype.clone(), len, validity) }
}

/// Packs [`ListViewArray`]s together into a chunked `ListViewArray`.
///
/// We use the existing arrays (chunks) to form a chunked array of `elements` (the child array).
///
/// The caller guarantees there are at least 2 chunks.
fn swizzle_list_chunks(
    chunks: &[ArrayRef],
    validity: Validity,
    elem_dtype: &DType,
) -> ListViewArray {
    let len: usize = chunks.iter().map(|c| c.len()).sum();

    assert_eq!(
        chunks[0]
            .dtype()
            .as_list_element_opt()
            .vortex_expect("DType was somehow not a list")
            .as_ref(),
        elem_dtype
    );

    // Since each list array in `chunks` has offsets local to each array, we can reuse the existing
    // array's child `elements` as the chunks and recompute offsets.

    let mut list_elements_chunks = Vec::with_capacity(chunks.len());
    let mut num_elements = 0;

    // TODO(connor)[ListView]: We could potentially choose a smaller type here, but that would make
    // this much more complicated.
    // We (somewhat arbitrarily) choose `u64` for our offsets and sizes here. These can always be
    // narrowed later by the compressor.
    let mut offsets = BufferMut::<u64>::with_capacity(len);
    let mut sizes = BufferMut::<u64>::with_capacity(len);

    for chunk in chunks {
        let chunk_array = chunk.to_listview();
        // By rebuilding as zero-copy to `List` and trimming all elements (to prevent gaps), we make
        // the final output `ListView` also zero-copyable to `List`.
        let chunk_array = chunk_array.rebuild(ListViewRebuildMode::MakeExact);

        // Add the `elements` of the current array as a new chunk.
        list_elements_chunks.push(chunk_array.elements().clone());

        // Cast offsets and sizes to `u64`.
        let offsets_arr = cast(
            chunk_array.offsets(),
            &DType::Primitive(PType::U64, Nullability::NonNullable),
        )
        .vortex_expect("Must be able to fit array offsets in u64")
        .to_primitive();

        let sizes_arr = cast(
            chunk_array.sizes(),
            &DType::Primitive(PType::U64, Nullability::NonNullable),
        )
        .vortex_expect("Must be able to fit array offsets in u64")
        .to_primitive();

        let offsets_slice = offsets_arr.as_slice::<u64>();
        let sizes_slice = sizes_arr.as_slice::<u64>();

        // Append offsets and sizes, adjusting offsets to point into the combined array.
        offsets.extend(offsets_slice.iter().map(|o| o + num_elements));
        sizes.extend(sizes_slice);

        num_elements += chunk_array.elements().len() as u64;
    }

    // SAFETY: elements are sliced from valid `ListViewArray`s (from `to_listview()`).
    let chunked_elements =
        unsafe { ChunkedArray::new_unchecked(list_elements_chunks, elem_dtype.clone()) }
            .into_array();

    let offsets = PrimitiveArray::new(offsets.freeze(), Validity::NonNullable).into_array();
    let sizes = PrimitiveArray::new(sizes.freeze(), Validity::NonNullable).into_array();

    // SAFETY:
    // - `offsets` and `sizes` are non-nullable u64 arrays of the same length
    // - Each `offset[i] + size[i]` list view is within bounds of elements array because it came
    //   from valid chunks
    // - Validity came from the outer chunked array so it must have the same length
    // - Since we made sure that all chunks were zero-copyable to a list above, we know that the
    //   final concatenated output is also zero-copyable to a list.
    unsafe {
        ListViewArray::new_unchecked(chunked_elements, offsets, sizes, validity)
            .with_zero_copy_to_list(true)
    }
}

#[cfg(test)]
mod tests {
    use std::sync::Arc;

    use vortex_buffer::buffer;
    use vortex_dtype::DType::{List, Primitive};
    use vortex_dtype::Nullability::NonNullable;
    use vortex_dtype::PType::I32;

    use crate::accessor::ArrayAccessor;
    use crate::arrays::{ChunkedArray, ListArray, StructArray, VarBinViewArray};
    use crate::validity::Validity;
    use crate::{IntoArray, ToCanonical};

    #[test]
    pub fn pack_nested_structs() {
        let struct_array = StructArray::try_new(
            ["a"].into(),
            vec![VarBinViewArray::from_iter_str(["foo", "bar", "baz", "quak"]).into_array()],
            4,
            Validity::NonNullable,
        )
        .unwrap();
        let dtype = struct_array.dtype().clone();
        let chunked = ChunkedArray::try_new(
            vec![
                ChunkedArray::try_new(vec![struct_array.to_array()], dtype.clone())
                    .unwrap()
                    .into_array(),
            ],
            dtype,
        )
        .unwrap()
        .into_array();
        let canonical_struct = chunked.to_struct();
        let canonical_varbin = canonical_struct.fields()[0].to_varbinview();
        let original_varbin = struct_array.fields()[0].to_varbinview();
        let orig_values = original_varbin
            .with_iterator(|it| it.map(|a| a.map(|v| v.to_vec())).collect::<Vec<_>>());
        let canon_values = canonical_varbin
            .with_iterator(|it| it.map(|a| a.map(|v| v.to_vec())).collect::<Vec<_>>());
        assert_eq!(orig_values, canon_values);
    }

    #[test]
    pub fn pack_nested_lists() {
        let l1 = ListArray::try_new(
            buffer![1, 2, 3, 4].into_array(),
            buffer![0, 3].into_array(),
            Validity::NonNullable,
        )
        .unwrap();

        let l2 = ListArray::try_new(
            buffer![5, 6].into_array(),
            buffer![0, 2].into_array(),
            Validity::NonNullable,
        )
        .unwrap();

        let chunked_list = ChunkedArray::try_new(
            vec![l1.clone().into_array(), l2.clone().into_array()],
            List(Arc::new(Primitive(I32, NonNullable)), NonNullable),
        );

        let canon_values = chunked_list.unwrap().to_listview();

        assert_eq!(l1.scalar_at(0), canon_values.scalar_at(0));
        assert_eq!(l2.scalar_at(0), canon_values.scalar_at(1));
    }
}