> ## Documentation Index
> Fetch the complete documentation index at: https://docs.lancedb.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Linear Combination Reranker

> Learn about LanceDB's deprecated Linear Combination Reranker for combining semantic and full-text search scores.

# Linear Combination Reranker

> **Note:** This reranker is deprecated. Use the `RRFReranker` if you need a score-based reranker.

The Linear Combination Reranker combines the results of semantic and full-text search using a linear combination of the scores. The weights for the linear combination can be specified, and defaults to 0.7, i.e, 70% weight for semantic search and 30% weight for full-text search.

> **Note:** Supported query type – Hybrid search only.

import lancedb
from lancedb.embeddings import get\_registry
from lancedb.pydantic import LanceModel, Vector
from lancedb.rerankers import LinearCombinationReranker

embedder = get\_registry().get("sentence-transformers").create()
db = lancedb.connect("\~/.lancedb")

class Schema(LanceModel):
    text: str = embedder.SourceField()
    vector: Vector(embedder.ndims()) = embedder.VectorField()

data = \[
    \{"text": "hello world"},
    \{"text": "goodbye world"},
]
tbl = db.create\_table("test", schema=Schema, mode="overwrite")
tbl.add(data)
reranker = LinearCombinationReranker()

\# Run hybrid search with a reranker
tbl.create\_fts\_index("text", replace=True)
result = (
    tbl.search("hello", query\_type="hybrid").rerank(reranker=reranker).to\_list()
)


## Accepted Arguments

| Argument | Type | Default | Description |
| - | - | - | - |
| `weight` | `float` | `0.7` | The weight to use for the semantic search score. The weight for the full-text search score is `1 - weight`. |
| `fill` | `float` | `1.0` | Score used when a result is missing from one side of the hybrid query. The default strongly penalizes missing vector or FTS matches. |
| `return_score` | `str` | `"relevance"` | Options are "relevance" or "all". The type of score to return. If "relevance", returns only `_relevance_score`. If "all", returns all scores from the vector and FTS search along with the relevance score. |

`weight` must be between `0` and `1`. If either the vector or FTS side returns no rows, the reranker
returns the non-empty side with `_relevance_score` attached rather than failing.

## Supported Scores for each query type

You can specify the type of scores you want the reranker to return. The following are the supported scores for each query type:

### Hybrid Search

| `return_score` | Status | Description |
| - | - | - |
| `relevance` | ✅ Supported | Results only have the `_relevance_score` column |
| `all` | ✅ Supported | Results have vector(`_distance`) and FTS(`score`) along with Hybrid Search score(`_distance`) |


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