Add common_gram token filter page #7923

_analyzers/token-filters/common_gram.md

@@ -0,0 +1,97 @@
+---
+layout: default
+title: common_grams
+parent: Token filters
+nav_order: 60
+---
+<!-- vale off -->
+# Common_grams token filter
+<!-- vale on -->
+The `common_grams` token filter in OpenSearch improves search relevance by keeping commonly occurring phrases (common grams) in the text. This is useful when dealing with languages or datasets where certain word combinations frequently occur and can impact the search relevance if treated as separate tokens. If any common words are present in the input string, this token filter generates both unigrams and bigrams.
+
+Using this token filter improves search relevance by keeping common phrases intact, it can help in matching queries more accurately, particularly for frequent word combinations. It also improves search precision by reducing the number of irrelevant matches.
+
+Using this filter requires careful selection and maintenance of the list of common words
+{: .warning}
+
+## Parameters
+
+The `common_grams` token filter can be configured with the following parameters:
+
+- `common_words`: A list of words that should be considered as common words. These words will be used to form common grams. If the `common_words` parameter is given an empty list, the `common_grams` token filter becomes a pass-through filter, meaning it doesn't modify the input tokens at all. (List of strings, _Required_)
+- `ignore_case`: Indicates whether the filter should ignore case differences when matching common words. Default is `false`. (Boolean, _Optional_)
+- `query_mode`: When set to `true` the following rules are applied:
+  - unigrams that are common_words are not included in the output.
+  - bigrams where a non-common word is followed by a common_word are retained in the output.
+  - unigrams of non-common words are excluded if they're immediately followed by a common_word.
+  - If a non-common word appears at the end of the text and is preceded by a common word, its unigram is also not included in the output. 
+  Default: `false` (Boolean, _Optional_)
+
+
+## Example
+
+The following example request creates a new index named `my_common_grams_index` and configures an analyzer with the `common_grams` filter:
+
+```json
+PUT /my_common_grams_index
+{
+  "settings": {
+    "analysis": {
+      "filter": {
+        "my_common_grams_filter": {
+          "type": "common_grams",
+          "common_words": ["a", "in", "for"],
+          "ignore_case": true,
+          "query_mode": true
+        }
+      },
+      "analyzer": {
+        "my_analyzer": {
+          "type": "custom",
+          "tokenizer": "standard",
+          "filter": [
+            "lowercase",
+            "my_common_grams_filter"
+          ]
+        }
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+## Generated tokens
+
+Use the following request to examine the tokens generated using the analyzer:
+
+```json
+GET /my_common_grams_index/_analyze
+{
+  "analyzer": "my_analyzer",
+  "text": "A quick black cat jumps over the lazy dog in the park"
+}
+```
+{% include copy-curl.html %}
+
+The response contains the generated tokens:
+
+```json
+{
+  "tokens": [
+    {"token": "a_quick","start_offset": 0,"end_offset": 7,"type": "gram","position": 0},
+    {"token": "quick","start_offset": 2,"end_offset": 7,"type": "<ALPHANUM>","position": 1},
+    {"token": "black","start_offset": 8,"end_offset": 13,"type": "<ALPHANUM>","position": 2},
+    {"token": "cat","start_offset": 14,"end_offset": 17,"type": "<ALPHANUM>","position": 3},
+    {"token": "jumps","start_offset": 18,"end_offset": 23,"type": "<ALPHANUM>","position": 4},
+    {"token": "over","start_offset": 24,"end_offset": 28,"type": "<ALPHANUM>","position": 5},
+    {"token": "the","start_offset": 29,"end_offset": 32,"type": "<ALPHANUM>","position": 6},
+    {"token": "lazy","start_offset": 33,"end_offset": 37,"type": "<ALPHANUM>","position": 7},
+    {"token": "dog_in","start_offset": 38,"end_offset": 44,"type": "gram","position": 8},
+    {"token": "in_the","start_offset": 42,"end_offset": 48,"type": "gram","position": 9},
+    {"token": "the","start_offset": 45,"end_offset": 48,"type": "<ALPHANUM>","position": 10},
+    {"token": "park","start_offset": 49,"end_offset": 53,"type": "<ALPHANUM>","position": 11}
+  ]
+}
+```
+

_analyzers/token-filters/index.md

@@ -20,7 +20,7 @@ Token filter | Underlying Lucene token filter|  Description
 `cjk_bigram` | [CJKBigramFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/cjk/CJKBigramFilter.html) | Forms bigrams of Chinese, Japanese, and Korean (CJK) tokens. 
 [`cjk_width`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/cjk-width/) | [CJKWidthFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/cjk/CJKWidthFilter.html) | Normalizes Chinese, Japanese, and Korean (CJK) tokens according to the following rules: <br> - Folds full-width ASCII character variants into their equivalent basic Latin characters. <br> - Folds half-width katakana character variants into their equivalent kana characters.
 [`classic`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/classic) | [ClassicFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/classic/ClassicFilter.html) | Performs optional post-processing on the tokens generated by the classic tokenizer. Removes possessives (`'s`) and removes `.` from acronyms.
-`common_grams` | [CommonGramsFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/commongrams/CommonGramsFilter.html) | Generates bigrams for a list of frequently occurring terms. The output contains both single terms and bigrams.
+[`common_grams`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/common_gram/) | [CommonGramsFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/commongrams/CommonGramsFilter.html) | Generates bigrams for a list of frequently occurring terms. The output contains both single terms and bigrams.
 `conditional` | [ConditionalTokenFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/ConditionalTokenFilter.html) | Applies an ordered list of token filters to tokens that match the conditions provided in a script.
 `decimal_digit` | [DecimalDigitFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/core/DecimalDigitFilter.html) | Converts all digits in the Unicode decimal number general category to basic Latin digits (0--9). 
 `delimited_payload` | [DelimitedPayloadTokenFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/payloads/DelimitedPayloadTokenFilter.html) | Separates a token stream into tokens with corresponding payloads, based on a provided delimiter. A token consists of all characters before the delimiter, and a payload consists of all characters after the delimiter. For example, if the delimiter is `|`, then for the string `foo|bar`, `foo` is the token and `bar` is the payload.