Add UniqueTerm token filter

analysis/token/unique/unique.go

@@ -0,0 +1,53 @@
+//  Copyright (c) 2018 Couchbase, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 		http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package unique
+
+import (
+	"github.com/blevesearch/bleve/analysis"
+	"github.com/blevesearch/bleve/registry"
+)
+
+const Name = "unique"
+
+// UniqueTermFilter retains only the tokens which mark the first occurence of
+// a term. Tokens whose term appears in a preceding token are dropped.
+type UniqueTermFilter struct{}
+
+func NewUniqueTermFilter() *UniqueTermFilter {
+	return &UniqueTermFilter{}
+}
+
+func (f *UniqueTermFilter) Filter(input analysis.TokenStream) analysis.TokenStream {
+	encounteredTerms := make(map[string]struct{}, len(input)/4)
+	j := 0
+	for _, token := range input {
+		term := string(token.Term)
+		if _, ok := encounteredTerms[term]; ok {
+			continue
+		}
+		encounteredTerms[term] = struct{}{}
+		input[j] = token
+		j++
+	}
+	return input[:j]
+}
+
+func UniqueTermFilterConstructor(config map[string]interface{}, cache *registry.Cache) (analysis.TokenFilter, error) {
+	return NewUniqueTermFilter(), nil
+}
+
+func init() {
+	registry.RegisterTokenFilter(Name, UniqueTermFilterConstructor)
+}

analysis/token/unique/unique_test.go

@@ -0,0 +1,84 @@
+//  Copyright (c) 2018 Couchbase, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 		http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package unique
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/blevesearch/bleve/analysis"
+)
+
+func TestUniqueTermFilter(t *testing.T) {
+	var tests = []struct {
+		input analysis.TokenStream
+		// expected indices of input which should be included in the output. We
+		// use indices instead of another TokenStream, since position/start/end
+		// should be preserved.
+		expectedIndices []int
+	}{
+		{
+			input:           tokenStream(),
+			expectedIndices: []int{},
+		},
+		{
+			input:           tokenStream("a"),
+			expectedIndices: []int{0},
+		},
+		{
+			input:           tokenStream("each", "term", "in", "this", "sentence", "is", "unique"),
+			expectedIndices: []int{0, 1, 2, 3, 4, 5, 6},
+		},
+		{
+			input:           tokenStream("Lui", "è", "alto", "e", "lei", "è", "bassa"),
+			expectedIndices: []int{0, 1, 2, 3, 4, 6},
+		},
+		{
+			input:           tokenStream("a", "a", "A", "a", "a", "A"),
+			expectedIndices: []int{0, 2},
+		},
+	}
+	uniqueTermFilter := NewUniqueTermFilter()
+	for _, test := range tests {
+		expected := subStream(test.input, test.expectedIndices)
+		actual := uniqueTermFilter.Filter(test.input)
+		if !reflect.DeepEqual(actual, expected) {
+			t.Errorf("expected %s \n\n got %s", expected, actual)
+		}
+	}
+}
+
+func tokenStream(termStrs ...string) analysis.TokenStream {
+	tokenStream := make([]*analysis.Token, len(termStrs))
+	index := 0
+	for i, termStr := range termStrs {
+		tokenStream[i] = &analysis.Token{
+			Term:     []byte(termStr),
+			Position: i + 1,
+			Start:    index,
+			End:      index + len(termStr),
+		}
+		index += len(termStr)
+	}
+	return analysis.TokenStream(tokenStream)
+}
+
+func subStream(stream analysis.TokenStream, indices []int) analysis.TokenStream {
+	result := make(analysis.TokenStream, len(indices))
+	for i, index := range indices {
+		result[i] = stream[index]
+	}
+	return result
+}