diff --git a/numpy_ext.py b/numpy_ext.py
index fd618ce..5da0a57 100644
--- a/numpy_ext.py
+++ b/numpy_ext.py
@@ -48,6 +48,7 @@
 ---------
 
 """
+from functools import partial
 from typing import Callable, Any, Union, Generator, Tuple, List
 
 import numpy as np
@@ -342,11 +343,14 @@ def rows_gen():
         if not skip_na:
             prepend_func = prepend_na
             if np.issubdtype(array.dtype, np.datetime64):
-                prepend_func = lambda arr, n: np.hstack((np.repeat(np.datetime64('NaT'), n), arr))
+
+                def prepend_func(arr, n):
+                    return np.hstack((np.repeat(np.datetime64('NaT'), n), arr))
 
             yield from (prepend_func(array[:i + 1], (window - 1) - i) for i in np.arange(window - 1))
 
-        yield from (array[i:i + window] for i in np.arange(array.size - (window - 1)))
+        starts = np.arange(array.size - (window - 1))
+        yield from (array[start:end] for start, end in zip(starts, starts + window))
 
     return np.array([row for row in rows_gen()]) if as_array else rows_gen()
 
@@ -395,14 +399,23 @@ def rolling_apply(func: Callable, window: int, *arrays: np.ndarray, n_jobs: int
         raise ValueError('Arrays must be the same length')
 
     def _apply_func_to_arrays(idxs):
-        return func(*[array[idxs.astype(np.int)] for array in arrays], **kwargs)
+        return func(*[array[idxs[0]:idxs[-1] + 1] for array in arrays], **kwargs)
 
-    rolls = rolling(np.arange(len(arrays[0])), window, skip_na=True)
+    array = arrays[0]
+    rolls = rolling(
+        array if len(arrays) == n_jobs == 1 else np.arange(len(array)),
+        window=window,
+        skip_na=True
+    )
 
     if n_jobs == 1:
-        arr = [_apply_func_to_arrays(idxs) for idxs in rolls]
+        if len(arrays) == 1:
+            arr = list(map(partial(func, **kwargs), rolls))
+        else:
+            arr = list(map(_apply_func_to_arrays, rolls))
     else:
-        arr = Parallel(n_jobs=n_jobs)(delayed(_apply_func_to_arrays)(idxs) for idxs in rolls)
+        f = delayed(_apply_func_to_arrays)
+        arr = Parallel(n_jobs=n_jobs)(f(idxs[[0, -1]]) for idxs in rolls)
 
     return prepend_na(arr, n=window - 1)
 
@@ -502,10 +515,20 @@ def expanding_apply(func: Callable, min_periods: int, *arrays: np.ndarray, n_job
     def _apply_func_to_arrays(idxs):
         return func(*[array[idxs.astype(np.int)] for array in arrays], **kwargs)
 
-    rolls = expanding(np.arange(len(arrays[0])), min_periods, skip_na=True)
+    array = arrays[0]
+    rolls = expanding(
+        array if len(arrays) == n_jobs == 1 else np.arange(len(array)),
+        min_periods=min_periods,
+        skip_na=True
+    )
+
     if n_jobs == 1:
-        arr = [_apply_func_to_arrays(idxs) for idxs in rolls]
+        if len(arrays) == 1:
+            arr = list(map(partial(func, **kwargs), rolls))
+        else:
+            arr = list(map(_apply_func_to_arrays, rolls))
     else:
-        arr = Parallel(n_jobs=n_jobs)(delayed(_apply_func_to_arrays)(idxs) for idxs in rolls)
+        f = delayed(_apply_func_to_arrays)
+        arr = Parallel(n_jobs=n_jobs)(map(f, rolls))
 
     return prepend_na(arr, n=min_periods - 1)
diff --git a/requirements.txt b/requirements.txt
index f5cee57..c9ebb99 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,2 +1,2 @@
-numpy~=1.16.4
-joblib~=0.14.1
+numpy==1.18.3
+joblib==0.14.1
diff --git a/setup.py b/setup.py
index a4018d7..1bf5a64 100644
--- a/setup.py
+++ b/setup.py
@@ -8,7 +8,7 @@
 
 
 def parse_reqs(path):
-    return [str(r.req) for r in parse_requirements(path, session=pip_session)]
+    return [r.requirement for r in parse_requirements(path, session=pip_session)]
 
 
 with open('README.md') as f: