build_reranking_dataset_BM25.py

from rank_bm25 import BM25Plus
import datasets
from sklearn.base import BaseEstimator
from sklearn.model_selection import GridSearchCV

from huggingface_hub import create_repo
from huggingface_hub.utils._errors import HfHubHTTPError


N_NEGATIVE_DOCS = 10
SPLIT = "test"

# Prepare documents
def create_text(example:dict) -> str:
    return "\n".join([example["title"], example["text"]])

documents = datasets.load_dataset("lyon-nlp/alloprof", "documents")["test"]
documents = documents.map(lambda x: {"text": create_text(x)})
documents = documents.rename_column("uuid", "doc_id")
documents = documents.remove_columns(["__index_level_0__", "title", "topic"])

# Prepare queries
queries = datasets.load_dataset("lyon-nlp/alloprof", "queries")[SPLIT]
queries = queries.rename_columns({"text": "queries", "relevant": "doc_id"})
queries = queries.remove_columns(["__index_level_0__", "answer", "id", "subject"])

# Optimize BM25 parameters
### Build sklearn estimator feature BM25
class BM25Estimator(BaseEstimator):

    def __init__(self, corpus_dataset:datasets.Dataset, *, k1:float=1.5, b:float=.75, delta:int=1):
        """Initialize BM25 estimator using the coprus dataset.
        The dataset must contain 2 columns:
        - "doc_id" : the documents ids
        - "text" : the document texts

        Args:
            corpus_dataset (datasets.Dataset): _description_
            k1 (float, optional): _description_. Defaults to 1.5.
            b (float, optional): _description_. Defaults to .75.
            delta (int, optional): _description_. Defaults to 1.
        """
        self.is_fitted_ = False

        self.corpus_dataset = corpus_dataset
        self.k1 = k1
        self.b = b
        self.delta=delta
        self.bm25 = None

    def tokenize_corpus(self, corpus:list[str]) -> list[str]:
        """Tokenize a corpus of strings

        Args:
            corpus (list[str]): the list of string to tokenize

        Returns:
            list[str]: the tokeinzed corpus
        """
        if isinstance(corpus, str):
            return corpus.lower().split()
        
        return [c.lower().split() for c in corpus]

    def fit(self, X=None, y=None):
        """Fits the BM25 using the dataset of documents
        Args are placeholders required by sklearn
        """
        tokenized_corpus = self.tokenize_corpus(self.corpus_dataset["text"])
        self.bm25 = BM25Plus(
            corpus=tokenized_corpus,
            k1=self.k1,
            b=self.b,
            delta=self.delta
        )
        self.is_fitted_ = True

        return self

    def predict(self, query:str, topN:int=10) -> list[str]:
        """Returns the best doc ids in order of best relevance first

        Args:
            query (str): _description_
            topN (int, optional): _description_. Defaults to 10.

        Returns:
            list[str]: _description_
        """
        if not self.is_fitted_:
            self.fit()

        tokenized_query = self.tokenize_corpus(query)
        best_docs = self.bm25.get_top_n(tokenized_query, self.corpus_dataset["text"], n=topN)
        doc_text2id = dict(list(zip(self.corpus_dataset["text"], self.corpus_dataset["doc_id"])))
        best_docs_ids = [doc_text2id[doc] for doc in best_docs]

        return best_docs_ids
    
    def score(self, queries:list[str], relevant_docs:list[list[str]]):
        """Scores the bm25 using the queries and relevant docs,
        using MRR as the metric.

        Args:
            queries (list[str]): list of queries
            relevant_docs (list[list[str]]): list of relevant documents ids for each query
        """
        best_docs_ids_preds = [self.predict(q, N_NEGATIVE_DOCS) for q in queries]
        best_docs_isrelevant = [
            [
                doc in rel_docs for doc in best_docs_ids_pred
                ]
            for best_docs_ids_pred, rel_docs in zip(best_docs_ids_preds, relevant_docs)
        ]
        mrrs = [self._compute_mrr(preds) for preds in best_docs_isrelevant]
        mrr = sum(mrrs)/len(mrrs)

        return mrr

    def _compute_mrr(self, predictions:list[bool]) -> float:
        """Compute the mrr considering a list of boolean predictions.
        Example:
            if predictions = [False, False, True, False], it would indicate
            that only the third document was labeled as relevant to the query

        Args:
            predictions (list[bool]): the binarized relevancy of predictions

        Returns:
            float: the mrr
        """
        if any(predictions):
            mrr = [1/(i+1) for i, pred in enumerate(predictions) if pred]
            mrr = sum(mrr)/len(mrr)
            return mrr
        else: 
            return 0

### Perform gridSearch to find best parameters for BM25
print("Optimizing BM25 parameters...")

params = {
    "k1":[1.25, 1.5, 1.75],
    "b": [.5, .75, 1.],
    "delta": [0, 1]
    }

gscv = GridSearchCV(BM25Estimator(documents), params, verbose=1)
gscv.fit(queries["queries"], queries["doc_id"])

print("Best parameterss :",  gscv.best_params_)
print("Best MRR score :",  gscv.best_score_)

# Build reranking dataset with positives and negative queries using best estimator
print("Generating reranking dataset...")
reranking_dataset = datasets.Dataset.from_dict(
    {
        "query": queries["queries"],
        "positive": queries["doc_id"],
        "negative": [
            [doc_id for doc_id in gscv.estimator.predict(q, N_NEGATIVE_DOCS) if doc_id not in relevant_ids]
            for q, relevant_ids in zip(queries["queries"], queries["doc_id"])
            ]
    })

# Push dataset to hub
### create HF repo
repo_id = "lyon-nlp/mteb-fr-reranking-alloprof-s2p"
try:
    create_repo(repo_id, repo_type="dataset")
except HfHubHTTPError as e:
    print("HF repo already exist")

### push to hub
reranking_dataset.push_to_hub(repo_id, config_name="queries", split=SPLIT)
documents.push_to_hub(repo_id, config_name="documents", split="test")