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 </pre><pre class="rust"><code><span class="kw">use </span>std::cmp::Ordering;
 <span class="kw">use </span>std::collections::BinaryHeap;
 <span class="kw">use </span>std::marker::PhantomData;

 <span class="kw">use crate</span>::{DocAddress, DocId, SegmentOrdinal, SegmentReader};

 <span class="doccomment">/// Contains a feature (field, score, etc.) of a document along with the document address.
 ///
 /// It has a custom implementation of `PartialOrd` that reverses the order. This is because the
 /// default Rust heap is a max heap, whereas a min heap is needed.
 ///
 /// Additionally, it guarantees stable sorting: in case of a tie on the feature, the document
 /// address is used.
 ///
 /// WARNING: equality is not what you would expect here.
 /// Two elements are equal if their feature is equal, and regardless of whether `doc`
 /// is equal. This should be perfectly fine for this usage, but let&#39;s make sure this
 /// struct is never public.
 </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>ComparableDoc&lt;T, D&gt; {
     <span class="kw">pub </span>feature: T,
     <span class="kw">pub </span>doc: D,
 }

 <span class="kw">impl</span>&lt;T: PartialOrd, D: PartialOrd&gt; PartialOrd <span class="kw">for </span>ComparableDoc&lt;T, D&gt; {
     <span class="kw">fn </span>partial_cmp(<span class="kw-2">&amp;</span><span class="self">self</span>, other: <span class="kw-2">&amp;</span><span class="self">Self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;Ordering&gt; {
         <span class="prelude-val">Some</span>(<span class="self">self</span>.cmp(other))
     }
 }

 <span class="kw">impl</span>&lt;T: PartialOrd, D: PartialOrd&gt; Ord <span class="kw">for </span>ComparableDoc&lt;T, D&gt; {
     <span class="attribute">#[inline]
     </span><span class="kw">fn </span>cmp(<span class="kw-2">&amp;</span><span class="self">self</span>, other: <span class="kw-2">&amp;</span><span class="self">Self</span>) -&gt; Ordering {
         <span class="comment">// Reversed to make BinaryHeap work as a min-heap
         </span><span class="kw">let </span>by_feature = other
             .feature
             .partial_cmp(<span class="kw-2">&amp;</span><span class="self">self</span>.feature)
             .unwrap_or(Ordering::Equal);

         <span class="kw">let </span>lazy_by_doc_address = || <span class="self">self</span>.doc.partial_cmp(<span class="kw-2">&amp;</span>other.doc).unwrap_or(Ordering::Equal);

         <span class="comment">// In case of a tie on the feature, we sort by ascending
         // `DocAddress` in order to ensure a stable sorting of the
         // documents.
         </span>by_feature.then_with(lazy_by_doc_address)
     }
 }

 <span class="kw">impl</span>&lt;T: PartialOrd, D: PartialOrd&gt; PartialEq <span class="kw">for </span>ComparableDoc&lt;T, D&gt; {
     <span class="kw">fn </span>eq(<span class="kw-2">&amp;</span><span class="self">self</span>, other: <span class="kw-2">&amp;</span><span class="self">Self</span>) -&gt; bool {
         <span class="self">self</span>.cmp(other) == Ordering::Equal
     }
 }

 <span class="kw">impl</span>&lt;T: PartialOrd, D: PartialOrd&gt; Eq <span class="kw">for </span>ComparableDoc&lt;T, D&gt; {}

 <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>TopCollector&lt;T&gt; {
     <span class="kw">pub </span>limit: usize,
     <span class="kw">pub </span>offset: usize,
     _marker: PhantomData&lt;T&gt;,
 }

 <span class="kw">impl</span>&lt;T&gt; TopCollector&lt;T&gt;
 <span class="kw">where </span>T: PartialOrd + Clone
 {
     <span class="doccomment">/// Creates a top collector, with a number of documents equal to &quot;limit&quot;.
     ///
     /// # Panics
     /// The method panics if limit is 0
     </span><span class="kw">pub fn </span>with_limit(limit: usize) -&gt; TopCollector&lt;T&gt; {
         <span class="macro">assert!</span>(limit &gt;= <span class="number">1</span>, <span class="string">&quot;Limit must be strictly greater than 0.&quot;</span>);
         <span class="self">Self </span>{
             limit,
             offset: <span class="number">0</span>,
             _marker: PhantomData,
         }
     }

     <span class="doccomment">/// Skip the first &quot;offset&quot; documents when collecting.
     ///
     /// This is equivalent to `OFFSET` in MySQL or PostgreSQL and `start` in
     /// Lucene&#39;s TopDocsCollector.
     </span><span class="kw">pub fn </span>and_offset(<span class="kw-2">mut </span><span class="self">self</span>, offset: usize) -&gt; TopCollector&lt;T&gt; {
         <span class="self">self</span>.offset = offset;
         <span class="self">self
     </span>}

     <span class="kw">pub fn </span>merge_fruits(
         <span class="kw-2">&amp;</span><span class="self">self</span>,
         children: Vec&lt;Vec&lt;(T, DocAddress)&gt;&gt;,
     ) -&gt; <span class="kw">crate</span>::Result&lt;Vec&lt;(T, DocAddress)&gt;&gt; {
         <span class="kw">if </span><span class="self">self</span>.limit == <span class="number">0 </span>{
             <span class="kw">return </span><span class="prelude-val">Ok</span>(Vec::new());
         }
         <span class="kw">let </span><span class="kw-2">mut </span>top_collector = BinaryHeap::new();
         <span class="kw">for </span>child_fruit <span class="kw">in </span>children {
             <span class="kw">for </span>(feature, doc) <span class="kw">in </span>child_fruit {
                 <span class="kw">if </span>top_collector.len() &lt; (<span class="self">self</span>.limit + <span class="self">self</span>.offset) {
                     top_collector.push(ComparableDoc { feature, doc });
                 } <span class="kw">else if let </span><span class="prelude-val">Some</span>(<span class="kw-2">mut </span>head) = top_collector.peek_mut() {
                     <span class="kw">if </span>head.feature &lt; feature {
                         <span class="kw-2">*</span>head = ComparableDoc { feature, doc };
                     }
                 }
             }
         }
         <span class="prelude-val">Ok</span>(top_collector
             .into_sorted_vec()
             .into_iter()
             .skip(<span class="self">self</span>.offset)
             .map(|cdoc| (cdoc.feature, cdoc.doc))
             .collect())
     }

     <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>for_segment&lt;F: PartialOrd&gt;(
         <span class="kw-2">&amp;</span><span class="self">self</span>,
         segment_id: SegmentOrdinal,
         <span class="kw">_</span>: <span class="kw-2">&amp;</span>SegmentReader,
     ) -&gt; TopSegmentCollector&lt;F&gt; {
         TopSegmentCollector::new(segment_id, <span class="self">self</span>.limit + <span class="self">self</span>.offset)
     }

     <span class="doccomment">/// Create a new TopCollector with the same limit and offset.
     ///
     /// Ideally we would use Into but the blanket implementation seems to cause the Scorer traits
     /// to fail.
     </span><span class="attribute">#[doc(hidden)]
     </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>into_tscore&lt;TScore: PartialOrd + Clone&gt;(<span class="self">self</span>) -&gt; TopCollector&lt;TScore&gt; {
         TopCollector {
             limit: <span class="self">self</span>.limit,
             offset: <span class="self">self</span>.offset,
             _marker: PhantomData,
         }
     }
 }

 <span class="doccomment">/// The Top Collector keeps track of the K documents
 /// sorted by type `T`.
 ///
 /// The implementation is based on a `BinaryHeap`.
 /// The theoretical complexity for collecting the top `K` out of `n` documents
 /// is `O(n log K)`.
 </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>TopSegmentCollector&lt;T&gt; {
     limit: usize,
     heap: BinaryHeap&lt;ComparableDoc&lt;T, DocId&gt;&gt;,
     segment_ord: u32,
 }

 <span class="kw">impl</span>&lt;T: PartialOrd&gt; TopSegmentCollector&lt;T&gt; {
     <span class="kw">fn </span>new(segment_ord: SegmentOrdinal, limit: usize) -&gt; TopSegmentCollector&lt;T&gt; {
         TopSegmentCollector {
             limit,
             heap: BinaryHeap::with_capacity(limit),
             segment_ord,
         }
     }
 }

 <span class="kw">impl</span>&lt;T: PartialOrd + Clone&gt; TopSegmentCollector&lt;T&gt; {
     <span class="kw">pub fn </span>harvest(<span class="self">self</span>) -&gt; Vec&lt;(T, DocAddress)&gt; {
         <span class="kw">let </span>segment_ord = <span class="self">self</span>.segment_ord;
         <span class="self">self</span>.heap
             .into_sorted_vec()
             .into_iter()
             .map(|comparable_doc| {
                 (
                     comparable_doc.feature,
                     DocAddress {
                         segment_ord,
                         doc_id: comparable_doc.doc,
                     },
                 )
             })
             .collect()
     }

     <span class="doccomment">/// Return true if more documents have been collected than the limit.
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>at_capacity(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; bool {
         <span class="self">self</span>.heap.len() &gt;= <span class="self">self</span>.limit
     }

     <span class="doccomment">/// Collects a document scored by the given feature
     ///
     /// It collects documents until it has reached the max capacity. Once it reaches capacity, it
     /// will compare the lowest scoring item with the given one and keep whichever is greater.
     </span><span class="attribute">#[inline]
     </span><span class="kw">pub fn </span>collect(<span class="kw-2">&amp;mut </span><span class="self">self</span>, doc: DocId, feature: T) {
         <span class="kw">if </span><span class="self">self</span>.at_capacity() {
             <span class="comment">// It&#39;s ok to unwrap as long as a limit of 0 is forbidden.
             </span><span class="kw">if let </span><span class="prelude-val">Some</span>(limit_feature) = <span class="self">self</span>.heap.peek().map(|head| head.feature.clone()) {
                 <span class="kw">if </span>limit_feature &lt; feature {
                     <span class="kw">if let </span><span class="prelude-val">Some</span>(<span class="kw-2">mut </span>head) = <span class="self">self</span>.heap.peek_mut() {
                         head.feature = feature;
                         head.doc = doc;
                     }
                 }
             }
         } <span class="kw">else </span>{
             <span class="comment">// we have not reached capacity yet, so we can just push the
             // element.
             </span><span class="self">self</span>.heap.push(ComparableDoc { feature, doc });
         }
     }
 }

 <span class="attribute">#[cfg(test)]
 </span><span class="kw">mod </span>tests {
     <span class="kw">use super</span>::{TopCollector, TopSegmentCollector};
     <span class="kw">use </span><span class="kw">crate</span>::DocAddress;

     <span class="attribute">#[test]
     </span><span class="kw">fn </span>test_top_collector_not_at_capacity() {
         <span class="kw">let </span><span class="kw-2">mut </span>top_collector = TopSegmentCollector::new(<span class="number">0</span>, <span class="number">4</span>);
         top_collector.collect(<span class="number">1</span>, <span class="number">0.8</span>);
         top_collector.collect(<span class="number">3</span>, <span class="number">0.2</span>);
         top_collector.collect(<span class="number">5</span>, <span class="number">0.3</span>);
         <span class="macro">assert_eq!</span>(
             top_collector.harvest(),
             <span class="macro">vec!</span>[
                 (<span class="number">0.8</span>, DocAddress::new(<span class="number">0</span>, <span class="number">1</span>)),
                 (<span class="number">0.3</span>, DocAddress::new(<span class="number">0</span>, <span class="number">5</span>)),
                 (<span class="number">0.2</span>, DocAddress::new(<span class="number">0</span>, <span class="number">3</span>))
             ]
         );
     }

     <span class="attribute">#[test]
     </span><span class="kw">fn </span>test_top_collector_at_capacity() {
         <span class="kw">let </span><span class="kw-2">mut </span>top_collector = TopSegmentCollector::new(<span class="number">0</span>, <span class="number">4</span>);
         top_collector.collect(<span class="number">1</span>, <span class="number">0.8</span>);
         top_collector.collect(<span class="number">3</span>, <span class="number">0.2</span>);
         top_collector.collect(<span class="number">5</span>, <span class="number">0.3</span>);
         top_collector.collect(<span class="number">7</span>, <span class="number">0.9</span>);
         top_collector.collect(<span class="number">9</span>, -<span class="number">0.2</span>);
         <span class="macro">assert_eq!</span>(
             top_collector.harvest(),
             <span class="macro">vec!</span>[
                 (<span class="number">0.9</span>, DocAddress::new(<span class="number">0</span>, <span class="number">7</span>)),
                 (<span class="number">0.8</span>, DocAddress::new(<span class="number">0</span>, <span class="number">1</span>)),
                 (<span class="number">0.3</span>, DocAddress::new(<span class="number">0</span>, <span class="number">5</span>)),
                 (<span class="number">0.2</span>, DocAddress::new(<span class="number">0</span>, <span class="number">3</span>))
             ]
         );
     }

     <span class="attribute">#[test]
     </span><span class="kw">fn </span>test_top_segment_collector_stable_ordering_for_equal_feature() {
         <span class="comment">// given that the documents are collected in ascending doc id order,
         // when harvesting we have to guarantee stable sorting in case of a tie
         // on the score
         </span><span class="kw">let </span>doc_ids_collection = [<span class="number">4</span>, <span class="number">5</span>, <span class="number">6</span>];
         <span class="kw">let </span>score = <span class="number">3.3f32</span>;

         <span class="kw">let </span><span class="kw-2">mut </span>top_collector_limit_2 = TopSegmentCollector::new(<span class="number">0</span>, <span class="number">2</span>);
         <span class="kw">for </span>id <span class="kw">in </span><span class="kw-2">&amp;</span>doc_ids_collection {
             top_collector_limit_2.collect(<span class="kw-2">*</span>id, score);
         }

         <span class="kw">let </span><span class="kw-2">mut </span>top_collector_limit_3 = TopSegmentCollector::new(<span class="number">0</span>, <span class="number">3</span>);
         <span class="kw">for </span>id <span class="kw">in </span><span class="kw-2">&amp;</span>doc_ids_collection {
             top_collector_limit_3.collect(<span class="kw-2">*</span>id, score);
         }

         <span class="macro">assert_eq!</span>(
             top_collector_limit_2.harvest(),
             top_collector_limit_3.harvest()[..<span class="number">2</span>].to_vec(),
         );
     }

     <span class="attribute">#[test]
     </span><span class="kw">fn </span>test_top_collector_with_limit_and_offset() {
         <span class="kw">let </span>collector = TopCollector::with_limit(<span class="number">2</span>).and_offset(<span class="number">1</span>);

         <span class="kw">let </span>results = collector
             .merge_fruits(<span class="macro">vec!</span>[<span class="macro">vec!</span>[
                 (<span class="number">0.9</span>, DocAddress::new(<span class="number">0</span>, <span class="number">1</span>)),
                 (<span class="number">0.8</span>, DocAddress::new(<span class="number">0</span>, <span class="number">2</span>)),
                 (<span class="number">0.7</span>, DocAddress::new(<span class="number">0</span>, <span class="number">3</span>)),
                 (<span class="number">0.6</span>, DocAddress::new(<span class="number">0</span>, <span class="number">4</span>)),
                 (<span class="number">0.5</span>, DocAddress::new(<span class="number">0</span>, <span class="number">5</span>)),
             ]])
             .unwrap();

         <span class="macro">assert_eq!</span>(
             results,
             <span class="macro">vec!</span>[(<span class="number">0.8</span>, DocAddress::new(<span class="number">0</span>, <span class="number">2</span>)), (<span class="number">0.7</span>, DocAddress::new(<span class="number">0</span>, <span class="number">3</span>)),]
         );
     }

     <span class="attribute">#[test]
     </span><span class="kw">fn </span>test_top_collector_with_limit_larger_than_set_and_offset() {
         <span class="kw">let </span>collector = TopCollector::with_limit(<span class="number">2</span>).and_offset(<span class="number">1</span>);

         <span class="kw">let </span>results = collector
             .merge_fruits(<span class="macro">vec!</span>[<span class="macro">vec!</span>[
                 (<span class="number">0.9</span>, DocAddress::new(<span class="number">0</span>, <span class="number">1</span>)),
                 (<span class="number">0.8</span>, DocAddress::new(<span class="number">0</span>, <span class="number">2</span>)),
             ]])
             .unwrap();

         <span class="macro">assert_eq!</span>(results, <span class="macro">vec!</span>[(<span class="number">0.8</span>, DocAddress::new(<span class="number">0</span>, <span class="number">2</span>)),]);
     }

     <span class="attribute">#[test]
     </span><span class="kw">fn </span>test_top_collector_with_limit_and_offset_larger_than_set() {
         <span class="kw">let </span>collector = TopCollector::with_limit(<span class="number">2</span>).and_offset(<span class="number">20</span>);

         <span class="kw">let </span>results = collector
             .merge_fruits(<span class="macro">vec!</span>[<span class="macro">vec!</span>[
                 (<span class="number">0.9</span>, DocAddress::new(<span class="number">0</span>, <span class="number">1</span>)),
                 (<span class="number">0.8</span>, DocAddress::new(<span class="number">0</span>, <span class="number">2</span>)),
             ]])
             .unwrap();

         <span class="macro">assert_eq!</span>(results, <span class="macro">vec!</span>[]);
     }
 }

 <span class="attribute">#[cfg(all(test, feature = <span class="string">&quot;unstable&quot;</span>))]
 </span><span class="kw">mod </span>bench {
     <span class="kw">use </span>test::Bencher;

     <span class="kw">use </span><span class="kw">super</span>::TopSegmentCollector;

     <span class="attribute">#[bench]
     </span><span class="kw">fn </span>bench_top_segment_collector_collect_not_at_capacity(b: <span class="kw-2">&amp;mut </span>Bencher) {
         <span class="kw">let </span><span class="kw-2">mut </span>top_collector = TopSegmentCollector::new(<span class="number">0</span>, <span class="number">400</span>);

         b.iter(|| {
             <span class="kw">for </span>i <span class="kw">in </span><span class="number">0</span>..<span class="number">100 </span>{
                 top_collector.collect(i, <span class="number">0.8</span>);
             }
         });
     }

     <span class="attribute">#[bench]
     </span><span class="kw">fn </span>bench_top_segment_collector_collect_at_capacity(b: <span class="kw-2">&amp;mut </span>Bencher) {
         <span class="kw">let </span><span class="kw-2">mut </span>top_collector = TopSegmentCollector::new(<span class="number">0</span>, <span class="number">100</span>);

         <span class="kw">for </span>i <span class="kw">in </span><span class="number">0</span>..<span class="number">100 </span>{
             top_collector.collect(i, <span class="number">0.8</span>);
         }

         b.iter(|| {
             <span class="kw">for </span>i <span class="kw">in </span><span class="number">0</span>..<span class="number">100 </span>{
                 top_collector.collect(i, <span class="number">0.8</span>);
             }
         });
     }

     <span class="attribute">#[bench]
     </span><span class="kw">fn </span>bench_top_segment_collector_collect_and_harvest_many_ties(b: <span class="kw-2">&amp;mut </span>Bencher) {
         b.iter(|| {
             <span class="kw">let </span><span class="kw-2">mut </span>top_collector = TopSegmentCollector::new(<span class="number">0</span>, <span class="number">100</span>);

             <span class="kw">for </span>i <span class="kw">in </span><span class="number">0</span>..<span class="number">100 </span>{
                 top_collector.collect(i, <span class="number">0.8</span>);
             }

             <span class="comment">// it would be nice to be able to do the setup N times but still
             // measure only harvest(). We can&#39;t since harvest() consumes
             // the top_collector.
             </span>top_collector.harvest()
         });
     }

     <span class="attribute">#[bench]
     </span><span class="kw">fn </span>bench_top_segment_collector_collect_and_harvest_no_tie(b: <span class="kw-2">&amp;mut </span>Bencher) {
         b.iter(|| {
             <span class="kw">let </span><span class="kw-2">mut </span>top_collector = TopSegmentCollector::new(<span class="number">0</span>, <span class="number">100</span>);
             <span class="kw">let </span><span class="kw-2">mut </span>score = <span class="number">1.0</span>;

             <span class="kw">for </span>i <span class="kw">in </span><span class="number">0</span>..<span class="number">100 </span>{
                 score += <span class="number">1.0</span>;
                 top_collector.collect(i, score);
             }

             <span class="comment">// it would be nice to be able to do the setup N times but still
             // measure only harvest(). We can&#39;t since harvest() consumes
             // the top_collector.
             </span>top_collector.harvest()
         });
     }
 }
 </code></pre></div>
 </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="tantivy" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html>