ce901a8870
this introduces new German light stemmer and moves the other pure Go german analysis components back in from the blevex package the libstemmer version of the stemmer will remain in blevex
117 lines
2.5 KiB
Go
117 lines
2.5 KiB
Go
// Copyright (c) 2017 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 de
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import (
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"bytes"
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"github.com/blevesearch/bleve/analysis"
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"github.com/blevesearch/bleve/registry"
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)
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const LightStemmerName = "stemmer_de_light"
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type GermanLightStemmerFilter struct {
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}
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func NewGermanLightStemmerFilter() *GermanLightStemmerFilter {
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return &GermanLightStemmerFilter{}
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}
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func (s *GermanLightStemmerFilter) Filter(input analysis.TokenStream) analysis.TokenStream {
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for _, token := range input {
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runes := bytes.Runes(token.Term)
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runes = stem(runes)
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token.Term = analysis.BuildTermFromRunes(runes)
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}
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return input
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}
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func stem(input []rune) []rune {
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for i, r := range input {
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switch r {
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case 'ä', 'à', 'á', 'â':
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input[i] = 'a'
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case 'ö', 'ò', 'ó', 'ô':
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input[i] = 'o'
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case 'ï', 'ì', 'í', 'î':
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input[i] = 'i'
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case 'ü', 'ù', 'ú', 'û':
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input[i] = 'u'
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}
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}
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input = step1(input)
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return step2(input)
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}
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func stEnding(ch rune) bool {
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switch ch {
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case 'b', 'd', 'f', 'g', 'h', 'k', 'l', 'm', 'n', 't':
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return true
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}
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return false
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}
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func step1(s []rune) []rune {
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l := len(s)
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if l > 5 && s[l-3] == 'e' && s[l-2] == 'r' && s[l-1] == 'n' {
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return s[:l-3]
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}
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if l > 4 && s[l-2] == 'e' {
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switch s[l-1] {
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case 'm', 'n', 'r', 's':
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return s[:l-2]
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}
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}
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if l > 3 && s[l-1] == 'e' {
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return s[:l-1]
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}
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if l > 3 && s[l-1] == 's' && stEnding(s[l-2]) {
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return s[:l-1]
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}
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return s
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}
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func step2(s []rune) []rune {
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l := len(s)
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if l > 5 && s[l-3] == 'e' && s[l-2] == 's' && s[l-1] == 't' {
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return s[:l-3]
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}
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if l > 4 && s[l-2] == 'e' && (s[l-1] == 'r' || s[l-1] == 'n') {
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return s[:l-2]
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}
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if l > 4 && s[l-2] == 's' && s[l-1] == 't' && stEnding(s[l-3]) {
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return s[:l-2]
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}
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return s
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}
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func GermanLightStemmerFilterConstructor(config map[string]interface{}, cache *registry.Cache) (analysis.TokenFilter, error) {
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return NewGermanLightStemmerFilter(), nil
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}
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func init() {
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registry.RegisterTokenFilter(LightStemmerName, GermanLightStemmerFilterConstructor)
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}
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