# Rerank QA Content

## Description

The Rerank operator is used to reorder the list of relevant documents for a query. It uses the [MS MARCO Cross-Encoders](https://www.sbert.net/docs/pretrained_cross-encoders.html#ms-marco) model to get the relevant scores and then reorders the documents.

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## Code Example

- Run with ops

```Python
from towhee import ops

op = ops.rerank()
res = op('What is Towhee?',
         ['Towhee is Towhee is a cutting-edge framework to deal with unstructure data.', 'I do not know about towhee', 'Towhee has many powerful operators.', 'The weather is good' ],
         0)
```

- Run a pipeline

```python
from towhee import ops, pipe, DataCollection

p = (pipe.input('query', 'doc', 'threshold')
         .map(('query', 'doc', 'threshold'), ('doc', 'score'), ops.rerank())
         .flat_map(('doc', 'score'), ('doc', 'score'), lambda x, y: [(i, j) for i, j in zip(x, y)])
         .output('query', 'doc', 'score')
     )

DataCollection(p('What is Towhee?',
                 ['Towhee is Towhee is a cutting-edge framework to deal with unstructure data.', 'I do not know about towhee', 'Towhee has many powerful operators.', 'The weather is good' ],
                 0)
              ).show()
```

<img src="./result.png" height="100px"/>

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## Factory Constructor

Create the operator via the following factory method

***towhee.rerank(model_name: str = 'cross-encoder/ms-marco-MiniLM-L-12-v2')***

**Parameters:**

   ***model_name***: str

​	The model name of CrossEncoder, you can set it according to the [Model List](https://www.sbert.net/docs/pretrained-models/ce-msmarco.html#models-performance).

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## Interface

This operator is used to sort the documents of the query content and return the score, and can also set a threshold to filter the results.

**Parameters:**

   ***query***: str

   The query content.

​	***docs***: list

   A list of sentences to check the correlation with the query content.

​	***threshold***: float

​    The threshold for filtering with score, defaults to none, i.e., no filtering.


<br />

**Return**: List[str], List[float]

The list of documents after rerank and the list of corresponding scores.