diff --git a/lib/data/features/transform.py b/lib/data/features/transform.py
index a96911d..6f65d5f 100644
--- a/lib/data/features/transform.py
+++ b/lib/data/features/transform.py
@@ -1,4 +1,5 @@
 import numpy as np
+import pandas as pd
 
 from abc import abstractmethod
 from typing import Callable, Iterable, List
@@ -11,7 +12,13 @@ def transform(iterable: Iterable, inplace: bool = True, columns: List[str] = Non
     else:
         transformed_iterable = iterable.copy()
 
-    transformed_iterable = transformed_iterable.fillna(method='bfill')
+    if isinstance(transformed_iterable, pd.DataFrame):
+        is_list = False
+        transformed_iterable.fillna(method='bfill', inplace=True)
+    else:
+        is_list = True
+        transformed_iterable = pd.DataFrame(transformed_iterable)
+        transformed_iterable.fillna(method='bfill', axis=1, inplace=True)
 
     if transform_fn is None:
         raise NotImplementedError()
@@ -23,6 +30,9 @@ def transform(iterable: Iterable, inplace: bool = True, columns: List[str] = Non
             transformed_iterable[column] = transform_fn(
                 transformed_iterable[column])
 
+    if is_list:
+        transformed_iterable = transformed_iterable.as_matrix()
+
     return transformed_iterable