community: add support for callable filters in FAISS (#16190)

- **Description:**
Filtering in a FAISS vectorstores is very inflexible and doesn't allow
that many use case. I think supporting callable like this enables a lot:
regular expressions, condition on multiple keys etc. **Note** I had to
manually alter a test. I don't understand if it was falty to begin with
or if there is something funky going on.
- **Issue:** None
- **Dependencies:** None
- **Twitter handle:** None

Signed-off-by: thiswillbeyourgithub <26625900+thiswillbeyourgithub@users.noreply.github.com>

docs/docs/integrations/vectorstores/faiss.ipynb

@@ -416,7 +416,7 @@
    "metadata": {},
    "source": [
     "## Similarity Search with filtering\n",
-    "FAISS vectorstore can also support filtering, since the FAISS does not natively support filtering we have to do it manually. This is done by first fetching more results than `k` and then filtering them. You can filter the documents based on metadata. You can also set the `fetch_k` parameter when calling any search method to set how many documents you want to fetch before filtering. Here is a small example:"
+    "FAISS vectorstore can also support filtering, since the FAISS does not natively support filtering we have to do it manually. This is done by first fetching more results than `k` and then filtering them. This filter is either a callble that takes as input a metadata dict and returns a bool, or a metadata dict where each missing key is ignored and each present k must be in a list of values. You can also set the `fetch_k` parameter when calling any search method to set how many documents you want to fetch before filtering. Here is a small example:"
    ]
   },
   {
@@ -480,6 +480,8 @@
    ],
    "source": [
     "results_with_scores = db.similarity_search_with_score(\"foo\", filter=dict(page=1))\n",
+    "# Or with a callable:\n",
+    "# results_with_scores = db.similarity_search_with_score(\"foo\", filter=lambda d: d[\"page\"] == 1)\n",
     "for doc, score in results_with_scores:\n",
     "    print(f\"Content: {doc.page_content}, Metadata: {doc.metadata}, Score: {score}\")"
    ]