Make new block from row indices.

cml/ports/source_adapters.py

@@ -98,6 +98,10 @@ class PandasBlock:
     def rows(self):
         return self.__data_block.shape[1]
 
+    def new_block_from_rows_index(self, indices: List[int]):
+        data_from = self.__data_block.loc[indices]
+        return PandasBlock(data_from)
+
     def new_block_from(self, column_values):
         data_from = self.__data_block.loc[self.__data_block["T"].isin(
             column_values)]