opensearch-docs-cn/_api-reference/rank-eval.md

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---
layout: default
title: Ranking evaluation
nav_order: 60
---
# Ranking evaluation
The [rank]({{site.url}}{{site.baseurl}}/opensearch/supported-field-types/rank/) eval endpoint allows you to evaluate the quality of ranked search results.
## Path and HTTP methods
```
GET <index_name>/_rank_eval
POST <index_name>/_rank_eval
```
## Query parameters
Query parameters are optional.
Parameter | Data type | Description
:--- | :--- | :---
ignore_unavailable | Boolean | Defaults to `false`. When set to `false` the response body will return an error if an index is closed or missing.
allow_no_indices | Boolean | Defaults to `true`. When set to `false` the response body will return an error if a wildcard expression points to indexes that are closed or missing.
expand_wildcards | String | Expand wildcard expressions for indexes that are `open`, `closed`, `hidden`, `none`, or `all`.
search_type | String | Set search type to either `query_then_fetch` or `dfs_query_then_fetch`.
## Request fields
The request body must contain at least one parameter.
Field Type | Description
:--- | :---
id | Document or template ID.
requests | Set multiple search requests within the request field section.
ratings | Document relevance score.
k | The number of documents returned per query. Default is set to 10.
relevant_rating_threshold | The threshold at which documents are considered relevant. Default is set to 1.
normalize | Discounted cumulative gain will be calculated when set to `true`.
maximum_relevance | Sets the maximum relevance score when using the expected reciprocal rank metric.
ignore_unlabeled | Defaults to `false`. Unlabeled documents are ignored when set to `true`.
template_id | Template ID.
params | Parameters used in the template.
#### Example request
````json
GET shakespeare/_rank_eval
{
"requests": [
{
"id": "books_query",
"request": {
"query": { "match": { "text": "thou" } }
},
"ratings": [
{ "_index": "shakespeare", "_id": "80", "rating": 0 },
{ "_index": "shakespeare", "_id": "115", "rating": 1 },
{ "_index": "shakespeare", "_id": "117", "rating": 2 }
]
},
{
"id": "words_query",
"request": {
"query": { "match": { "text": "art" } }
},
"ratings": [
{ "_index": "shakespeare", "_id": "115", "rating": 2 }
]
}
]
}
````
{% include copy-curl.html %}
#### Example response
````json
{
"rank_eval": {
"metric_score": 0.7,
"details": {
"query_1": {
"metric_score": 0.9,
"unrated_docs": [
{
"_index": "shakespeare",
"_id": "1234567"
}, ...
],
"hits": [
{
"hit": {
"_index": "shakespeare",
"_type": "page",
"_id": "1234567",
"_score": 5.123456789
},
"rating": 1
}, ...
],
"metric_details": {
"precision": {
"relevant_docs_retrieved": 3,
"docs_retrieved": 6
}
}
},
"query_2": { [... ] }
},
"failures": { [... ] }
}
}
````