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| </pre><pre class="rust"><code><span class="kw">use </span>serde::{Deserialize, Serialize}; |
| |
| <span class="kw">use </span><span class="kw">crate</span>::fieldnorm::FieldNormReader; |
| <span class="kw">use </span><span class="kw">crate</span>::query::Explanation; |
| <span class="kw">use crate</span>::{Score, Searcher, Term}; |
| |
| <span class="kw">const </span>K1: Score = <span class="number">1.2</span>; |
| <span class="kw">const </span>B: Score = <span class="number">0.75</span>; |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>idf(doc_freq: u64, doc_count: u64) -> Score { |
| <span class="macro">assert!</span>(doc_count >= doc_freq, <span class="string">"{} >= {}"</span>, doc_count, doc_freq); |
| <span class="kw">let </span>x = ((doc_count - doc_freq) <span class="kw">as </span>Score + <span class="number">0.5</span>) / (doc_freq <span class="kw">as </span>Score + <span class="number">0.5</span>); |
| (<span class="number">1.0 </span>+ x).ln() |
| } |
| |
| <span class="kw">fn </span>cached_tf_component(fieldnorm: u32, average_fieldnorm: Score) -> Score { |
| K1 * (<span class="number">1.0 </span>- B + B * fieldnorm <span class="kw">as </span>Score / average_fieldnorm) |
| } |
| |
| <span class="kw">fn </span>compute_tf_cache(average_fieldnorm: Score) -> [Score; <span class="number">256</span>] { |
| <span class="kw">let </span><span class="kw-2">mut </span>cache: [Score; <span class="number">256</span>] = [<span class="number">0.0</span>; <span class="number">256</span>]; |
| <span class="kw">for </span>(fieldnorm_id, cache_mut) <span class="kw">in </span>cache.iter_mut().enumerate() { |
| <span class="kw">let </span>fieldnorm = FieldNormReader::id_to_fieldnorm(fieldnorm_id <span class="kw">as </span>u8); |
| <span class="kw-2">*</span>cache_mut = cached_tf_component(fieldnorm, average_fieldnorm); |
| } |
| cache |
| } |
| |
| <span class="attribute">#[derive(Clone, PartialEq, Debug, Serialize, Deserialize)] |
| </span><span class="kw">pub struct </span>Bm25Params { |
| <span class="kw">pub </span>idf: Score, |
| <span class="kw">pub </span>avg_fieldnorm: Score, |
| } |
| |
| <span class="attribute">#[derive(Clone)] |
| </span><span class="kw">pub struct </span>Bm25Weight { |
| idf_explain: Explanation, |
| weight: Score, |
| cache: [Score; <span class="number">256</span>], |
| average_fieldnorm: Score, |
| } |
| |
| <span class="kw">impl </span>Bm25Weight { |
| <span class="kw">pub fn </span>boost_by(<span class="kw-2">&</span><span class="self">self</span>, boost: Score) -> Bm25Weight { |
| Bm25Weight { |
| idf_explain: <span class="self">self</span>.idf_explain.clone(), |
| weight: <span class="self">self</span>.weight * boost, |
| cache: <span class="self">self</span>.cache, |
| average_fieldnorm: <span class="self">self</span>.average_fieldnorm, |
| } |
| } |
| |
| <span class="kw">pub fn </span>for_terms(searcher: <span class="kw-2">&</span>Searcher, terms: <span class="kw-2">&</span>[Term]) -> <span class="kw">crate</span>::Result<Bm25Weight> { |
| <span class="macro">assert!</span>(!terms.is_empty(), <span class="string">"Bm25 requires at least one term"</span>); |
| <span class="kw">let </span>field = terms[<span class="number">0</span>].field(); |
| <span class="kw">for </span>term <span class="kw">in </span><span class="kw-2">&</span>terms[<span class="number">1</span>..] { |
| <span class="macro">assert_eq!</span>( |
| term.field(), |
| field, |
| <span class="string">"All terms must belong to the same field." |
| </span>); |
| } |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>total_num_tokens = <span class="number">0u64</span>; |
| <span class="kw">let </span><span class="kw-2">mut </span>total_num_docs = <span class="number">0u64</span>; |
| <span class="kw">for </span>segment_reader <span class="kw">in </span>searcher.segment_readers() { |
| <span class="kw">let </span>inverted_index = segment_reader.inverted_index(field)<span class="question-mark">?</span>; |
| total_num_tokens += inverted_index.total_num_tokens(); |
| total_num_docs += u64::from(segment_reader.max_doc()); |
| } |
| <span class="kw">let </span>average_fieldnorm = total_num_tokens <span class="kw">as </span>Score / total_num_docs <span class="kw">as </span>Score; |
| |
| <span class="kw">if </span>terms.len() == <span class="number">1 </span>{ |
| <span class="kw">let </span>term_doc_freq = searcher.doc_freq(<span class="kw-2">&</span>terms[<span class="number">0</span>])<span class="question-mark">?</span>; |
| <span class="prelude-val">Ok</span>(Bm25Weight::for_one_term( |
| term_doc_freq, |
| total_num_docs, |
| average_fieldnorm, |
| )) |
| } <span class="kw">else </span>{ |
| <span class="kw">let </span><span class="kw-2">mut </span>idf_sum: Score = <span class="number">0.0</span>; |
| <span class="kw">for </span>term <span class="kw">in </span>terms { |
| <span class="kw">let </span>term_doc_freq = searcher.doc_freq(term)<span class="question-mark">?</span>; |
| idf_sum += idf(term_doc_freq, total_num_docs); |
| } |
| <span class="kw">let </span>idf_explain = Explanation::new(<span class="string">"idf"</span>, idf_sum); |
| <span class="prelude-val">Ok</span>(Bm25Weight::new(idf_explain, average_fieldnorm)) |
| } |
| } |
| |
| <span class="kw">pub fn </span>for_one_term( |
| term_doc_freq: u64, |
| total_num_docs: u64, |
| avg_fieldnorm: Score, |
| ) -> Bm25Weight { |
| <span class="kw">let </span>idf = idf(term_doc_freq, total_num_docs); |
| <span class="kw">let </span><span class="kw-2">mut </span>idf_explain = |
| Explanation::new(<span class="string">"idf, computed as log(1 + (N - n + 0.5) / (n + 0.5))"</span>, idf); |
| idf_explain.add_const( |
| <span class="string">"n, number of docs containing this term"</span>, |
| term_doc_freq <span class="kw">as </span>Score, |
| ); |
| idf_explain.add_const(<span class="string">"N, total number of docs"</span>, total_num_docs <span class="kw">as </span>Score); |
| Bm25Weight::new(idf_explain, avg_fieldnorm) |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>new(idf_explain: Explanation, average_fieldnorm: Score) -> Bm25Weight { |
| <span class="kw">let </span>weight = idf_explain.value() * (<span class="number">1.0 </span>+ K1); |
| Bm25Weight { |
| idf_explain, |
| weight, |
| cache: compute_tf_cache(average_fieldnorm), |
| average_fieldnorm, |
| } |
| } |
| |
| <span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>score(<span class="kw-2">&</span><span class="self">self</span>, fieldnorm_id: u8, term_freq: u32) -> Score { |
| <span class="self">self</span>.weight * <span class="self">self</span>.tf_factor(fieldnorm_id, term_freq) |
| } |
| |
| <span class="kw">pub fn </span>max_score(<span class="kw-2">&</span><span class="self">self</span>) -> Score { |
| <span class="self">self</span>.score(<span class="number">255u8</span>, <span class="number">2_013_265_944</span>) |
| } |
| |
| <span class="attribute">#[inline] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>tf_factor(<span class="kw-2">&</span><span class="self">self</span>, fieldnorm_id: u8, term_freq: u32) -> Score { |
| <span class="kw">let </span>term_freq = term_freq <span class="kw">as </span>Score; |
| <span class="kw">let </span>norm = <span class="self">self</span>.cache[fieldnorm_id <span class="kw">as </span>usize]; |
| term_freq / (term_freq + norm) |
| } |
| |
| <span class="kw">pub fn </span>explain(<span class="kw-2">&</span><span class="self">self</span>, fieldnorm_id: u8, term_freq: u32) -> Explanation { |
| <span class="comment">// The explain format is directly copied from Lucene's. |
| // (So, Kudos to Lucene) |
| </span><span class="kw">let </span>score = <span class="self">self</span>.score(fieldnorm_id, term_freq); |
| |
| <span class="kw">let </span>norm = <span class="self">self</span>.cache[fieldnorm_id <span class="kw">as </span>usize]; |
| <span class="kw">let </span>term_freq = term_freq <span class="kw">as </span>Score; |
| <span class="kw">let </span>right_factor = term_freq / (term_freq + norm); |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>tf_explanation = Explanation::new( |
| <span class="string">"freq / (freq + k1 * (1 - b + b * dl / avgdl))"</span>, |
| right_factor, |
| ); |
| |
| tf_explanation.add_const(<span class="string">"freq, occurrences of term within document"</span>, term_freq); |
| tf_explanation.add_const(<span class="string">"k1, term saturation parameter"</span>, K1); |
| tf_explanation.add_const(<span class="string">"b, length normalization parameter"</span>, B); |
| tf_explanation.add_const( |
| <span class="string">"dl, length of field"</span>, |
| FieldNormReader::id_to_fieldnorm(fieldnorm_id) <span class="kw">as </span>Score, |
| ); |
| tf_explanation.add_const(<span class="string">"avgdl, average length of field"</span>, <span class="self">self</span>.average_fieldnorm); |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>explanation = Explanation::new(<span class="string">"TermQuery, product of..."</span>, score); |
| explanation.add_detail(Explanation::new(<span class="string">"(K1+1)"</span>, K1 + <span class="number">1.0</span>)); |
| explanation.add_detail(<span class="self">self</span>.idf_explain.clone()); |
| explanation.add_detail(tf_explanation); |
| explanation |
| } |
| } |
| |
| <span class="attribute">#[cfg(test)] |
| </span><span class="kw">mod </span>tests { |
| |
| <span class="kw">use </span><span class="kw">super</span>::idf; |
| <span class="kw">use crate</span>::{assert_nearly_equals, Score}; |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_idf() { |
| <span class="kw">let </span>score: Score = <span class="number">2.0</span>; |
| <span class="macro">assert_nearly_equals!</span>(idf(<span class="number">1</span>, <span class="number">2</span>), score.ln()); |
| } |
| } |
| </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> |
