feat: add a filterable count_rows to all the lancedb APIs (#913)

A `count_rows` method that takes a filter was recently added to
`LanceTable`. This PR adds it everywhere else except `RemoteTable` (that
will come soon).

python/lancedb/remote/table.py

@@ -37,6 +37,9 @@ class RemoteTable(Table):
     def __repr__(self) -> str:
         return f"RemoteTable({self._conn.db_name}.{self._name})"
 
+    def __len__(self) -> int:
+        self.count_rows(None)
+
     @cached_property
     def schema(self) -> pa.Schema:
         """The [Arrow Schema](https://arrow.apache.org/docs/python/api/datatypes.html#)
@@ -409,6 +412,13 @@ class RemoteTable(Table):
             "compact_files() is not supported on the LanceDB cloud"
         )
 
+    def count_rows(self, filter: Optional[str] = None) -> int:
+        # payload = {"filter": filter}
+        # self._conn._client.post(f"/v1/table/{self._name}/count_rows/", data=payload)
+        return NotImplementedError(
+            "count_rows() is not yet supported on the LanceDB cloud"
+        )
+
 
 def add_index(tbl: pa.Table, i: int) -> pa.Table:
     return tbl.add_column(

python/lancedb/table.py

@@ -176,6 +176,18 @@ class Table(ABC):
         """
         raise NotImplementedError
 
+    @abstractmethod
+    def count_rows(self, filter: Optional[str] = None) -> int:
+        """
+        Count the number of rows in the table.
+
+        Parameters
+        ----------
+        filter: str, optional
+            A SQL where clause to filter the rows to count.
+        """
+        raise NotImplementedError
+
     def to_pandas(self) -> "pd.DataFrame":
         """Return the table as a pandas DataFrame.
 
@@ -925,14 +937,6 @@ class LanceTable(Table):
         self._ref.dataset = ds
 
     def count_rows(self, filter: Optional[str] = None) -> int:
-        """
-        Count the number of rows in the table.
-
-        Parameters
-        ----------
-        filter: str, optional
-            A SQL where clause to filter the rows to count.
-        """
         return self._dataset.count_rows(filter)
 
     def __len__(self):