class FlagEmbeddingReranker(BaseNodePostprocessor):
"""Flag Embedding Reranker."""
model: str = Field(description="BAAI Reranker model name.")
top_n: int = Field(description="Number of nodes to return sorted by score.")
use_fp16: bool = Field(description="Whether to use fp16 for inference.")
_model: Any = PrivateAttr()
def __init__(
self,
top_n: int = 2,
model: str = "BAAI/bge-reranker-large",
use_fp16: bool = False,
) -> None:
try:
from FlagEmbedding import FlagReranker
except ImportError:
raise ImportError(
"Cannot import FlagReranker package, please install it: ",
"pip install git+https://github.com/FlagOpen/FlagEmbedding.git",
)
self._model = FlagReranker(
model,
use_fp16=use_fp16,
)
super().__init__(top_n=top_n, model=model, use_fp16=use_fp16)
@classmethod
def class_name(cls) -> str:
return "FlagEmbeddingReranker"
def _postprocess_nodes(
self,
nodes: List[NodeWithScore],
query_bundle: Optional[QueryBundle] = None,
) -> List[NodeWithScore]:
dispatch_event = dispatcher.get_dispatch_event()
dispatch_event(
ReRankStartEvent(
query=query_bundle,
nodes=nodes,
top_n=self.top_n,
model_name=self.model,
)
)
if query_bundle is None:
raise ValueError("Missing query bundle in extra info.")
if len(nodes) == 0:
return []
query_and_nodes = [
(
query_bundle.query_str,
node.node.get_content(metadata_mode=MetadataMode.EMBED),
)
for node in nodes
]
with self.callback_manager.event(
CBEventType.RERANKING,
payload={
EventPayload.NODES: nodes,
EventPayload.MODEL_NAME: self.model,
EventPayload.QUERY_STR: query_bundle.query_str,
EventPayload.TOP_K: self.top_n,
},
) as event:
scores = self._model.compute_score(query_and_nodes)
# a single node passed into compute_score returns a float
if isinstance(scores, float):
scores = [scores]
assert len(scores) == len(nodes)
for node, score in zip(nodes, scores):
node.score = score
new_nodes = sorted(nodes, key=lambda x: -x.score if x.score else 0)[
: self.top_n
]
event.on_end(payload={EventPayload.NODES: new_nodes})
dispatch_event(ReRankEndEvent(nodes=new_nodes))
return new_nodes