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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,122 @@ | ||
| // https://artem.krylysov.com/blog/2020/07/28/lets-build-a-full-text-search-engine/ | ||
| package main | ||
|
|
||
| import ( | ||
| "strings" | ||
| "unicode" | ||
|
|
||
| snowballeng "github.com/kljensen/snowball/english" | ||
| ) | ||
|
|
||
| type index map[string][]int | ||
|
|
||
| func (idx index) add(titles []string) { | ||
| for id, title := range titles { | ||
| for _, token := range analyze(title) { | ||
| if contains(idx[token], id) { | ||
| continue | ||
| } | ||
| idx[token] = append(idx[token], id) | ||
| } | ||
| } | ||
| } | ||
|
|
||
| func analyze(text string) []string { | ||
| tokens := tokenize(text) | ||
| tokens = toLower(tokens) | ||
| tokens = removeCommonWords(tokens) | ||
| tokens = stem(tokens) | ||
| return tokens | ||
| } | ||
|
|
||
| func tokenize(text string) []string { | ||
| return strings.FieldsFunc(text, func(r rune) bool { | ||
| return !unicode.IsLetter(r) && !unicode.IsNumber(r) | ||
| }) | ||
| } | ||
|
|
||
| func toLower(tokens []string) []string { | ||
| r := make([]string, len(tokens)) | ||
| for i, token := range tokens { | ||
| r[i] = strings.ToLower(token) | ||
| } | ||
| return r | ||
| } | ||
|
|
||
| var stopWords = map[string]struct{}{ | ||
| "a": {}, | ||
| "and": {}, | ||
| "be": {}, | ||
| "have": {}, | ||
| "i": {}, | ||
| "in": {}, | ||
| "of": {}, | ||
| "that": {}, | ||
| "the": {}, | ||
| "to": {}, | ||
| } | ||
|
|
||
| func removeCommonWords(tokens []string) []string { | ||
| r := make([]string, 0, len(tokens)) | ||
| for _, token := range tokens { | ||
| if _, ok := stopWords[token]; !ok { | ||
| r = append(r, token) | ||
| } | ||
| } | ||
| return r | ||
| } | ||
|
|
||
| func stem(tokens []string) []string { | ||
| r := make([]string, len(tokens)) | ||
| for i, token := range tokens { | ||
| r[i] = snowballeng.Stem(token, false) | ||
| } | ||
| return r | ||
| } | ||
|
|
||
| func contains(slice []int, val int) bool { | ||
| for _, s := range slice { | ||
| if s == val { | ||
| return true | ||
| } | ||
| } | ||
| return false | ||
| } | ||
|
|
||
| func intersection(a, b []int) []int { | ||
| maxLen := len(a) | ||
| if len(b) > maxLen { | ||
| maxLen = len(b) | ||
| } | ||
|
|
||
| r := make([]int, 0, maxLen) | ||
| var i, j int | ||
| for i < len(a) && j < len(b) { | ||
| if a[i] < b[j] { | ||
| i++ | ||
| } else if a[i] > b[j] { | ||
| j++ | ||
| } else { | ||
| r = append(r, a[i]) | ||
| i++ | ||
| j++ | ||
| } | ||
| } | ||
| return r | ||
| } | ||
|
|
||
| func (idx index) search(text string) []int { | ||
| var r []int | ||
| for _, token := range analyze(text) { | ||
| if ids, ok := idx[token]; ok { | ||
| if r == nil { | ||
| r = ids | ||
| } else { | ||
| r = intersection(r, ids) | ||
| } | ||
| } else { | ||
| return nil | ||
| } | ||
| } | ||
| return r | ||
| } |