partners[chroma]: add retrieval of embedding vectors (#28290)

This PR adds an additional method to `Chroma` to retrieve the embedding
vectors, besides the most relevant Documents. This is sometimes of use
when you need to run a postprocessing algorithm on the retrieved results
based on the vectors, which has been the case for me lately.

Example issue (discussion) requesting this change:
https://github.com/langchain-ai/langchain/discussions/20383

---------

Co-authored-by: ccurme <chester.curme@gmail.com>

libs/partners/chroma/langchain_chroma/vectorstores.py

@@ -53,6 +53,17 @@ def _results_to_docs_and_scores(results: Any) -> List[Tuple[Document, float]]:
     ]
 
 
+def _results_to_docs_and_vectors(results: Any) -> List[Tuple[Document, np.ndarray]]:
+    return [
+        (Document(page_content=result[0], metadata=result[1] or {}), result[2])
+        for result in zip(
+            results["documents"][0],
+            results["metadatas"][0],
+            results["embeddings"][0],
+        )
+    ]
+
+
 Matrix = Union[List[List[float]], List[np.ndarray], np.ndarray]
 
 
@@ -687,6 +698,51 @@ class Chroma(VectorStore):
 
         return _results_to_docs_and_scores(results)
 
+    def similarity_search_with_vectors(
+        self,
+        query: str,
+        k: int = DEFAULT_K,
+        filter: Optional[Dict[str, str]] = None,
+        where_document: Optional[Dict[str, str]] = None,
+        **kwargs: Any,
+    ) -> List[Tuple[Document, np.ndarray]]:
+        """Run similarity search with Chroma with vectors.
+
+        Args:
+            query: Query text to search for.
+            k: Number of results to return. Defaults to 4.
+            filter: Filter by metadata. Defaults to None.
+            where_document: dict used to filter by the documents.
+                    E.g. {$contains: {"text": "hello"}}.
+            kwargs: Additional keyword arguments to pass to Chroma collection query.
+
+        Returns:
+            List of documents most similar to the query text and
+            embedding vectors for each.
+        """
+        include = ["documents", "metadatas", "embeddings"]
+        if self._embedding_function is None:
+            results = self.__query_collection(
+                query_texts=[query],
+                n_results=k,
+                where=filter,
+                where_document=where_document,
+                include=include,
+                **kwargs,
+            )
+        else:
+            query_embedding = self._embedding_function.embed_query(query)
+            results = self.__query_collection(
+                query_embeddings=[query_embedding],
+                n_results=k,
+                where=filter,
+                where_document=where_document,
+                include=include,
+                **kwargs,
+            )
+
+        return _results_to_docs_and_vectors(results)
+
     def _select_relevance_score_fn(self) -> Callable[[float], float]:
         """Select the relevance score function based on collections distance metric.
 

libs/partners/chroma/tests/integration_tests/test_vectorstores.py

@@ -92,6 +92,24 @@ def test_chroma_with_metadatas_with_scores() -> None:
     assert output == [(Document(page_content="foo", metadata={"page": "0"}), 0.0)]
 
 
+def test_chroma_with_metadatas_with_vectors() -> None:
+    """Test end to end construction and scored search."""
+    texts = ["foo", "bar", "baz"]
+    metadatas = [{"page": str(i)} for i in range(len(texts))]
+    embeddings = ConsistentFakeEmbeddings()
+    docsearch = Chroma.from_texts(
+        collection_name="test_collection",
+        texts=texts,
+        embedding=embeddings,
+        metadatas=metadatas,
+    )
+    vec_1 = embeddings.embed_query(texts[0])
+    output = docsearch.similarity_search_with_vectors("foo", k=1)
+    docsearch.delete_collection()
+    assert output[0][0] == Document(page_content="foo", metadata={"page": "0"})
+    assert (output[0][1] == vec_1).all()
+
+
 def test_chroma_with_metadatas_with_scores_using_vector() -> None:
     """Test end to end construction and scored search, using embedding vector."""
     texts = ["foo", "bar", "baz"]