## Coverage Report

#### Created: 2024-10-13 08:39

    /Users/andrewlamb/Software/datafusion/datafusion/functions-aggregate-common/src/merge_arrays.rs

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    // Licensed to the Apache Software Foundation (ASF) under one
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    // or more contributor license agreements.  See the NOTICE file
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    // distributed with this work for additional information
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    // regarding copyright ownership.  The ASF licenses this file
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    // to you under the Apache License, Version 2.0 (the
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    // "License"); you may not use this file except in compliance
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    // with the License.  You may obtain a copy of the License at
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    //
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    //   http://www.apache.org/licenses/LICENSE-2.0
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    //
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    // Unless required by applicable law or agreed to in writing,
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    // software distributed under the License is distributed on an
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    // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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    // KIND, either express or implied.  See the License for the
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    // specific language governing permissions and limitations
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    // under the License.
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    use arrow::compute::SortOptions;
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    use datafusion_common::utils::compare_rows;
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    use datafusion_common::{exec_err, ScalarValue};
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    use std::cmp::Ordering;
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    use std::collections::{BinaryHeap, VecDeque};
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    /// This is a wrapper struct to be able to correctly merge `ARRAY_AGG` data from
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    /// multiple partitions using `BinaryHeap`. When used inside `BinaryHeap`, this
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    /// struct returns smallest `CustomElement`, where smallest is determined by
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    /// `ordering` values (`Vec<ScalarValue>`) according to `sort_options`.
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    #[derive(Debug, PartialEq, Eq)]
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    struct CustomElement<'a> {
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        /// Stores the partition this entry came from
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        branch_idx: usize,
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        /// Values to merge
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        value: ScalarValue,
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        // Comparison "key"
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        ordering: Vec<ScalarValue>,
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        /// Options defining the ordering semantics
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        sort_options: &'a [SortOptions],
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    }
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    impl<'a> CustomElement<'a> {
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        fn new(
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            branch_idx: usize,
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            value: ScalarValue,
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            ordering: Vec<ScalarValue>,
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            sort_options: &'a [SortOptions],
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        ) -> Self {
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            Self {
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                branch_idx,
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                value,
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                ordering,
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                sort_options,
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            }
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        }
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        fn ordering(
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            &self,
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            current: &[ScalarValue],
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            target: &[ScalarValue],
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        ) -> datafusion_common::Result<Ordering> {
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            // Calculate ordering according to `sort_options`
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            compare_rows(current, target, self.sort_options)
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        }
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    }
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    // Overwrite ordering implementation such that
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    // - `self.ordering` values are used for comparison,
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    // - When used inside `BinaryHeap` it is a min-heap.
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    impl<'a> Ord for CustomElement<'a> {
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        fn cmp(&self, other: &Self) -> Ordering {
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            // Compares according to custom ordering
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            self.ordering(&self.ordering, &other.ordering)
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                // Convert max heap to min heap
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                .map(|ordering| ordering.reverse())
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                // This function return error, when `self.ordering` and `other.ordering`
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                // have different types (such as one is `ScalarValue::Int64`, other is `ScalarValue::Float32`)
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                // Here this case won't happen, because data from each partition will have same type
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                .unwrap()
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        }
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    }
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    impl<'a> PartialOrd for CustomElement<'a> {
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        fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
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            Some(self.cmp(other))
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        }
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    }
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    /// This functions merges `values` array (`&[Vec<ScalarValue>]`) into single array `Vec<ScalarValue>`
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    /// Merging done according to ordering values stored inside `ordering_values` (`&[Vec<Vec<ScalarValue>>]`)
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    /// Inner `Vec<ScalarValue>` in the `ordering_values` can be thought as ordering information for the
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    /// each `ScalarValue` in the `values` array.
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    /// Desired ordering specified by `sort_options` argument (Should have same size with inner `Vec<ScalarValue>`
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    /// of the `ordering_values` array).
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    ///
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    /// As an example
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    /// values can be \[
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    ///      \[1, 2, 3, 4, 5\],
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    ///      \[1, 2, 3, 4\],
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    ///      \[1, 2, 3, 4, 5, 6\],
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    /// \]
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    /// In this case we will be merging three arrays (doesn't have to be same size)
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    /// and produce a merged array with size 15 (sum of 5+4+6)
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    /// Merging will be done according to ordering at `ordering_values` vector.
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    /// As an example `ordering_values` can be [
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    ///      \[(1, a), (2, b), (3, b), (4, a), (5, b) \],
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    ///      \[(1, a), (2, b), (3, b), (4, a) \],
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    ///      \[(1, b), (2, c), (3, d), (4, e), (5, a), (6, b) \],
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    /// ]
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    /// For each ScalarValue in the `values` we have a corresponding `Vec<ScalarValue>` (like timestamp of it)
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    /// for the example above `sort_options` will have size two, that defines ordering requirement of the merge.
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    /// Inner `Vec<ScalarValue>`s of the `ordering_values` will be compared according `sort_options` (Their sizes should match)
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    pub fn merge_ordered_arrays(
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        // We will merge values into single `Vec<ScalarValue>`.
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        values: &mut [VecDeque<ScalarValue>],
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        // `values` will be merged according to `ordering_values`.
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        // Inner `Vec<ScalarValue>` can be thought as ordering information for the
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        // each `ScalarValue` in the values`.
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        ordering_values: &mut [VecDeque<Vec<ScalarValue>>],
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        // Defines according to which ordering comparisons should be done.
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        sort_options: &[SortOptions],
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    ) -> datafusion_common::Result<(Vec<ScalarValue>, Vec<Vec<ScalarValue>>)> {
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        // Keep track the most recent data of each branch, in binary heap data structure.
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        let mut heap = BinaryHeap::<CustomElement>::new();
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        if values.len() != ordering_values.len()
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            || values
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                .iter()
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                .zip(ordering_values.iter())
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                .any(|(vals, ordering_vals)| vals.len() != ordering_vals.len())
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        {
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            return exec_err!(
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                "Expects values arguments and/or ordering_values arguments to have same size"
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            );
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        }
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        let n_branch = values.len();
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        let mut merged_values = vec![];
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        let mut merged_orderings = vec![];
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        // Continue iterating the loop until consuming data of all branches.
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        loop {
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            let minimum = if let Some(minimum) = heap.pop() {
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                minimum
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            } else {
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                // Heap is empty, fill it with the next entries from each branch.
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                for branch_idx in 0..n_branch {
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                    if let Some(orderings) = ordering_values[branch_idx].pop_front() {
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                        // Their size should be same, we can safely .unwrap here.
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                        let value = values[branch_idx].pop_front().unwrap();
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                        // Push the next element to the heap:
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                        heap.push(CustomElement::new(
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                            branch_idx,
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                            value,
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                            orderings,
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                            sort_options,
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                        ));
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                    }
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                    // If None, we consumed this branch, skip it.
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                }
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                // Now we have filled the heap, get the largest entry (this will be
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                // the next element in merge).
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                if let Some(minimum) = heap.pop() {
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                    minimum
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                } else {
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                    // Heap is empty, this means that all indices are same with
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                    // `end_indices`. We have consumed all of the branches, merge
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                    // is completed, exit from the loop:
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                    break;
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                }
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            };
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            let CustomElement {
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                branch_idx,
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                value,
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                ordering,
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                ..
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            } = minimum;
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            // Add minimum value in the heap to the result
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            merged_values.push(value);
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            merged_orderings.push(ordering);
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            // If there is an available entry, push next entry in the most
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            // recently consumed branch to the heap.
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            if let Some(orderings) = ordering_values[branch_idx].pop_front() {
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                // Their size should be same, we can safely .unwrap here.
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                let value = values[branch_idx].pop_front().unwrap();
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                // Push the next element to the heap:
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                heap.push(CustomElement::new(
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                    branch_idx,
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                    value,
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                    orderings,
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                    sort_options,
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                ));
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            }
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        }
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        Ok((merged_values, merged_orderings))
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    }