[Backport 2.18] Add edge n-gram token filter docs #7980

_analyzers/token-filters/edge-ngram.md

@@ -0,0 +1,111 @@
+---
+layout: default
+title: Edge n-gram
+parent: Token filters
+nav_order: 120
+---
+# Edge n-gram token filter
+The `edge_ngram` token filter is very similar to the `ngram` token filter, where a particular string is split into substrings of different lengths. The `edge_ngram` token filter, however, generates n-grams (substrings) only from the beginning (edge) of a token. It's particularly useful in scenarios like autocomplete or prefix matching, where you want to match the beginning of words or phrases as the user types them.
+
+## Parameters
+
+The `edge_ngram` token filter can be configured with the following parameters.
+
+Parameter | Required/Optional | Data type | Description
+:--- | :--- | :--- | :--- 
+`min_gram` | Optional | Integer | The minimum length of the n-grams that will be generated. Default is `1`.
+`max_gram` | Optional | Integer | The maximum length of the n-grams that will be generated. Default is `1` for the `edge_ngram` filter and `2` for custom token filters. Avoid setting this parameter to a low value. If the value is set too low, only very short n-grams will be generated and the search term will not be found. For example, if `max_gram` is set to `3` and you index the word "banana", the longest generated token will be "ban". If the user searches for "banana", no matches will be returned. You can use the `truncate` token filter as a search analyzer to mitigate this risk.
+`preserve_original` | Optional | Boolean | Includes the original token in the output. Default is `false` .
+
+## Example
+
+The following example request creates a new index named `edge_ngram_example` and configures an analyzer with the `edge_ngram` filter:
+
+```json
+PUT /edge_ngram_example
+{
+  "settings": {
+    "analysis": {
+      "filter": {
+        "my_edge_ngram": {
+          "type": "edge_ngram",
+          "min_gram": 3,
+          "max_gram": 4
+        }
+      },
+      "analyzer": {
+        "my_analyzer": {
+          "type": "custom",
+          "tokenizer": "standard",
+          "filter": ["lowercase", "my_edge_ngram"]
+        }
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+## Generated tokens
+
+Use the following request to examine the tokens generated using the analyzer:
+
+```json
+POST /edge_ngram_example/_analyze
+{
+  "analyzer": "my_analyzer",
+  "text": "slow green turtle"
+}
+```
+{% include copy-curl.html %}
+
+The response contains the generated tokens:
+
+```json
+{
+  "tokens": [
+    {
+      "token": "slo",
+      "start_offset": 0,
+      "end_offset": 4,
+      "type": "<ALPHANUM>",
+      "position": 0
+    },
+    {
+      "token": "slow",
+      "start_offset": 0,
+      "end_offset": 4,
+      "type": "<ALPHANUM>",
+      "position": 0
+    },
+    {
+      "token": "gre",
+      "start_offset": 5,
+      "end_offset": 10,
+      "type": "<ALPHANUM>",
+      "position": 1
+    },
+    {
+      "token": "gree",
+      "start_offset": 5,
+      "end_offset": 10,
+      "type": "<ALPHANUM>",
+      "position": 1
+    },
+    {
+      "token": "tur",
+      "start_offset": 11,
+      "end_offset": 17,
+      "type": "<ALPHANUM>",
+      "position": 2
+    },
+    {
+      "token": "turt",
+      "start_offset": 11,
+      "end_offset": 17,
+      "type": "<ALPHANUM>",
+      "position": 2
+    }
+  ]
+}
+```

_analyzers/token-filters/index.md

@@ -25,8 +25,8 @@ Token filter | Underlying Lucene token filter|  Description
 [`decimal_digit`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/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`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/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 preceding the delimiter, and a payload consists of all characters following the delimiter. For example, if the delimiter is `|`, then for the string `foo|bar`, `foo` is the token and `bar` is the payload. 
 [`delimited_term_freq`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/delimited-term-frequency/) | [DelimitedTermFrequencyTokenFilter](https://lucene.apache.org/core/9_7_0/analysis/common/org/apache/lucene/analysis/miscellaneous/DelimitedTermFrequencyTokenFilter.html) | Separates a token stream into tokens with corresponding term frequencies, based on a provided delimiter. A token consists of all characters before the delimiter, and a term frequency is the integer after the delimiter. For example, if the delimiter is `|`, then for the string `foo|5`, `foo` is the token and `5` is the term frequency.
-[`dictionary_decompounder`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/dictionary-decompounder/) | [DictionaryCompoundWordTokenFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/compound/DictionaryCompoundWordTokenFilter.html) | Splits compound words into their constituent parts based on a predefined dictionary. Useful for many Germanic languages.
-`edge_ngram` | [EdgeNGramTokenFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/ngram/EdgeNGramTokenFilter.html) | Tokenizes the given token into edge n-grams (n-grams that start at the beginning of the token) of lengths between `min_gram` and `max_gram`. Optionally, keeps the original token.
+[`dictionary_decompounder`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/dictionary-decompounder/) | [DictionaryCompoundWordTokenFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/compound/DictionaryCompoundWordTokenFilter.html) | Decomposes compound words found in many Germanic languages.
+[`edge_ngram`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/edge-ngram/) | [EdgeNGramTokenFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/ngram/EdgeNGramTokenFilter.html) | Tokenizes the given token into edge n-grams (n-grams that start at the beginning of the token) of lengths between `min_gram` and `max_gram`. Optionally, keeps the original token.
 `elision` | [ElisionFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/util/ElisionFilter.html) | Removes the specified [elisions](https://en.wikipedia.org/wiki/Elision) from the beginning of tokens. For example, changes `l'avion` (the plane) to `avion` (plane).
 `fingerprint` | [FingerprintFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/FingerprintFilter.html) | Sorts and deduplicates the token list and concatenates tokens into a single token.
 `flatten_graph` | [FlattenGraphFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/core/FlattenGraphFilter.html) | Flattens a token graph produced by a graph token filter, such as `synonym_graph` or `word_delimiter_graph`, making the graph suitable for indexing.