![Marty Schoch](/assets/img/avatar_default.png)
the logic of how a phrase search works should be an internal detail of the phrase searcher. further, these changes will allow proper scoring of phrase matches, which require access to the underlying searcher objects, which were hidden in the previous approach.
296 lines
7.9 KiB
Go
296 lines
7.9 KiB
Go
// Copyright (c) 2014 Couchbase, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// 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, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package searcher
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import (
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"fmt"
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"math"
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"github.com/blevesearch/bleve/index"
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"github.com/blevesearch/bleve/search"
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)
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type PhraseSearcher struct {
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indexReader index.IndexReader
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mustSearcher *ConjunctionSearcher
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queryNorm float64
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currMust *search.DocumentMatch
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slop int
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terms []string
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initialized bool
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}
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func NewPhraseSearcher(indexReader index.IndexReader, terms []string, field string, options search.SearcherOptions) (*PhraseSearcher, error) {
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options.IncludeTermVectors = true
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termSearchers := make([]search.Searcher, 0)
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for _, term := range terms {
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if term != "" {
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ts, err := NewTermSearcher(indexReader, term, field, 1.0, options)
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if err != nil {
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return nil, fmt.Errorf("phrase searcher error building term searcher: %v", err)
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}
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termSearchers = append(termSearchers, ts)
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}
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}
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mustSearcher, err := NewConjunctionSearcher(indexReader, termSearchers, options)
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if err != nil {
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return nil, fmt.Errorf("phrase searcher error building conjunction searcher: %v", err)
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}
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// build our searcher
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rv := PhraseSearcher{
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indexReader: indexReader,
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mustSearcher: mustSearcher,
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terms: terms,
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}
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rv.computeQueryNorm()
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return &rv, nil
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}
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func (s *PhraseSearcher) computeQueryNorm() {
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// first calculate sum of squared weights
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sumOfSquaredWeights := 0.0
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if s.mustSearcher != nil {
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sumOfSquaredWeights += s.mustSearcher.Weight()
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}
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// now compute query norm from this
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s.queryNorm = 1.0 / math.Sqrt(sumOfSquaredWeights)
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// finally tell all the downstream searchers the norm
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if s.mustSearcher != nil {
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s.mustSearcher.SetQueryNorm(s.queryNorm)
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}
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}
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func (s *PhraseSearcher) initSearchers(ctx *search.SearchContext) error {
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err := s.advanceNextMust(ctx)
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if err != nil {
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return err
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}
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s.initialized = true
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return nil
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}
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func (s *PhraseSearcher) advanceNextMust(ctx *search.SearchContext) error {
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var err error
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if s.mustSearcher != nil {
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s.currMust, err = s.mustSearcher.Next(ctx)
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if err != nil {
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return err
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}
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}
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return nil
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}
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func (s *PhraseSearcher) Weight() float64 {
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return s.mustSearcher.Weight()
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}
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func (s *PhraseSearcher) SetQueryNorm(qnorm float64) {
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s.mustSearcher.SetQueryNorm(qnorm)
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}
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func (s *PhraseSearcher) Next(ctx *search.SearchContext) (*search.DocumentMatch, error) {
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if !s.initialized {
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err := s.initSearchers(ctx)
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if err != nil {
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return nil, err
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}
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}
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for s.currMust != nil {
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// check this match against phrase constraints
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rv := s.checkCurrMustMatch(ctx)
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// prepare for next iteration (either loop or subsequent call to Next())
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err := s.advanceNextMust(ctx)
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if err != nil {
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return nil, err
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}
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// if match satisfied phrase constraints return it as a hit
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if rv != nil {
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return rv, nil
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}
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}
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return nil, nil
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}
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// checkCurrMustMatch is soley concerned with determining if the DocumentMatch
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// pointed to by s.currMust (which satisifies the pre-condition searcher)
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// also satisfies the phase constraints. if so, it returns a DocumentMatch
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// for this document, otherwise nil
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func (s *PhraseSearcher) checkCurrMustMatch(ctx *search.SearchContext) *search.DocumentMatch {
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rvftlm := make(search.FieldTermLocationMap, 0)
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freq := 0
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// typically we would expect there to only actually be results in
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// one field, but we allow for this to not be the case
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// but, we note that phrase constraints can only be satisfied within
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// a single field, so we can check them each independently
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for field, tlm := range s.currMust.Locations {
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f, rvtlm := s.checkCurrMustMatchField(ctx, tlm)
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if f > 0 {
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freq += f
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rvftlm[field] = rvtlm
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}
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}
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if freq > 0 {
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// return match
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rv := s.currMust
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rv.Locations = rvftlm
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return rv
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}
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return nil
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}
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// checkCurrMustMatchField is soley concerned with determining if one particular
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// field within the currMust DocumentMatch Locations satisfies the phase
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// constraints (possibly more than once). if so, the number of times it was
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// satisfied, and these locations are returned. otherwise 0 and either
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// a nil or empty TermLocationMap
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func (s *PhraseSearcher) checkCurrMustMatchField(ctx *search.SearchContext, tlm search.TermLocationMap) (int, search.TermLocationMap) {
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paths := findPhrasePaths(0, nil, s.terms, tlm, nil, 0)
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rv := make(search.TermLocationMap, len(s.terms))
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for _, p := range paths {
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p.MergeInto(rv)
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}
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return len(paths), rv
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}
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type phrasePart struct {
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term string
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loc *search.Location
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}
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type phrasePath []*phrasePart
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func (p phrasePath) MergeInto(in search.TermLocationMap) {
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for _, pp := range p {
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in[pp.term] = append(in[pp.term], pp.loc)
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}
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}
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// findPhrasePaths is a function to identify phase matches from a set of known
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// term locations. the implementation is recursive, so care must be taken
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// with arguments and return values.
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//
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// prev - the previous location, nil on first invocation
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// phraseTerms - slice containing the phrase terms themselves
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// may contain empty string as placeholder (don't care)
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// tlm - the Term Location Map containing all relevant term locations
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// offset - the offset from the previous that this next term must match
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// p - the current path being explored (appended to in recursive calls)
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// this is the primary state being built during the traversal
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//
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// returns slice of paths, or nil if invocation did not find any successul paths
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func findPhrasePaths(prevPos uint64, ap search.ArrayPositions, phraseTerms []string, tlm search.TermLocationMap, p phrasePath, remainingSlop int) []phrasePath {
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// no more terms
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if len(phraseTerms) < 1 {
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return []phrasePath{p}
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}
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car := phraseTerms[0]
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cdr := phraseTerms[1:]
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// empty term is treated as match (continue)
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if car == "" {
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nextPos := prevPos + 1
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if prevPos == 0 {
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// if prevPos was 0, don't set it to 1 (as thats not a real abs pos)
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nextPos = 0 // don't advance nextPos if prevPos was 0
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}
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return findPhrasePaths(nextPos, ap, cdr, tlm, p, remainingSlop)
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}
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// locations for this term
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locations := tlm[car]
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var rv []phrasePath
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for _, loc := range locations {
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if prevPos != 0 && !loc.ArrayPositions.Equals(ap) {
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// if the array positions are wrong, can't match, try next location
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continue
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}
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// compute distance from previous phrase term
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dist := 0
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if prevPos != 0 {
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dist = editDistance(prevPos+1, loc.Pos)
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}
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// if enough slop reamining, continue recursively
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if prevPos == 0 || (remainingSlop-dist) >= 0 {
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// this location works, add it to the path (but not for empty term)
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px := append(p, &phrasePart{term: car, loc: loc})
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rv = append(rv, findPhrasePaths(loc.Pos, loc.ArrayPositions, cdr, tlm, px, remainingSlop-dist)...)
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}
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}
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return rv
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}
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func editDistance(p1, p2 uint64) int {
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dist := int(p1 - p2)
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if dist < 0 {
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return -dist
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}
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return dist
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}
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func (s *PhraseSearcher) Advance(ctx *search.SearchContext, ID index.IndexInternalID) (*search.DocumentMatch, error) {
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if !s.initialized {
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err := s.initSearchers(ctx)
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if err != nil {
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return nil, err
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}
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}
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var err error
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s.currMust, err = s.mustSearcher.Advance(ctx, ID)
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if err != nil {
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return nil, err
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}
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return s.Next(ctx)
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}
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func (s *PhraseSearcher) Count() uint64 {
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// for now return a worst case
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return s.mustSearcher.Count()
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}
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func (s *PhraseSearcher) Close() error {
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if s.mustSearcher != nil {
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err := s.mustSearcher.Close()
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if err != nil {
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return err
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}
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}
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return nil
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}
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func (s *PhraseSearcher) Min() int {
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return 0
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}
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func (s *PhraseSearcher) DocumentMatchPoolSize() int {
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return s.mustSearcher.DocumentMatchPoolSize() + 1
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}
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