Feature faiss delete (#8135)

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Replace this comment with:
- Description: docstore had two main method: add and search, however,
dealing with docstore sometimes requires deleting an entry from
docstore. So I have added a simple delete method that deletes items from
docstore. Additionally, I have added the delete method to faiss
vectorstore for the very same reason.
  - Issue: NA
  - Dependencies: NA
  - Tag maintainer:  @rlancemartin, @eyurtsev
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---------

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

libs/langchain/langchain/docstore/base.py

@@ -1,6 +1,6 @@
 """Interface to access to place that stores documents."""
 from abc import ABC, abstractmethod
-from typing import Dict, Union
+from typing import Dict, List, Union
 
 from langchain.docstore.document import Document
 
@@ -16,6 +16,10 @@ class Docstore(ABC):
         If page does not exist, return similar entries.
         """
 
+    def delete(self, ids: List) -> None:
+        """Deleting IDs from in memory dictionary."""
+        raise NotImplementedError
+
 
 class AddableMixin(ABC):
     """Mixin class that supports adding texts."""

libs/langchain/langchain/docstore/in_memory.py

@@ -1,5 +1,5 @@
 """Simple in memory docstore in the form of a dict."""
-from typing import Dict, Optional, Union
+from typing import Dict, List, Optional, Union
 
 from langchain.docstore.base import AddableMixin, Docstore
 from langchain.docstore.document import Document
@@ -26,6 +26,14 @@ class InMemoryDocstore(Docstore, AddableMixin):
             raise ValueError(f"Tried to add ids that already exist: {overlapping}")
         self._dict = {**self._dict, **texts}
 
+    def delete(self, ids: List) -> None:
+        """Deleting IDs from in memory dictionary."""
+        overlapping = set(ids).intersection(self._dict)
+        if not overlapping:
+            raise ValueError(f"Tried to delete ids that does not  exist: {ids}")
+        for _id in ids:
+            self._dict.pop(_id)
+
     def search(self, search: str) -> Union[str, Document]:
         """Search via direct lookup.
 

libs/langchain/langchain/vectorstores/faiss.py

@@ -468,6 +468,36 @@ class FAISS(VectorStore):
         )
         return docs
 
+    def delete(self, ids: Optional[List[str]] = None, **kwargs: Any) -> Optional[bool]:
+        """Delete by ID. These are the IDs in the vectorstore.
+
+        Args:
+            ids: List of ids to delete.
+
+        Returns:
+            Optional[bool]: True if deletion is successful,
+            False otherwise, None if not implemented.
+        """
+        if ids is None:
+            raise ValueError("No ids provided to delete.")
+
+        overlapping = set(ids).intersection(self.index_to_docstore_id.values())
+        if not overlapping:
+            raise ValueError("ids do not exist in the current object")
+
+        _reversed_index = {v: k for k, v in self.index_to_docstore_id.items()}
+
+        index_to_delete = [_reversed_index[i] for i in ids]
+
+        # Removing ids from index.
+        self.index.remove_ids(np.array(index_to_delete, dtype=np.int64))
+        for _id in index_to_delete:
+            del self.index_to_docstore_id[_id]
+
+        # Remove items from docstore.
+        self.docstore.delete(ids)
+        return True
+
     def merge_from(self, target: FAISS) -> None:
         """Merge another FAISS object with the current one.