Update Q.75, 76, 81, 84, 85, 87

iamyifan · iamyifan · commit e72a3d9f355d · 2021-12-17T16:41:42.000+08:00
Update alternative solutions with sliding_window_view (NumPy &gt;= 1.20.0).
diff --git a/source/exercises100.ktx b/source/exercises100.ktx
@@ -1017,7 +1017,7 @@ print(A)
 How to compute averages using a sliding window over an array? (★★★)
 
 < h75
-hint: np.cumsum
+hint: np.cumsum, from numpy.lib.stride_tricks import sliding_window_view (np>=1.20.0)
 
 < a75
 # Author: Jaime Fernández del Río
@@ -1029,11 +1029,19 @@ def moving_average(a, n=3) :
 Z = np.arange(20)
 print(moving_average(Z, n=3))
 
+# Author: Jeff Luo (@Jeff1999)
+# make sure your NumPy >= 1.20.0
+
+from numpy.lib.stride_tricks import sliding_window_view
+
+Z = np.arange(20)
+print(sliding_window_view(Z, window_shape=3).mean(axis=-1))
+
 < q76
 Consider a one-dimensional array Z, build a two-dimensional array whose first row is (Z[0],Z[1],Z[2]) and each subsequent row is  shifted by 1 (last row should be (Z[-3],Z[-2],Z[-1]) (★★★)
 
 < h76
-hint: from numpy.lib import stride_tricks
+hint: from numpy.lib import stride_tricks, from numpy.lib.stride_tricks import sliding_window_view (np>=1.20.0)
 
 < a76
 # Author: Joe Kington / Erik Rigtorp
@@ -1046,6 +1054,11 @@ def rolling(a, window):
 Z = rolling(np.arange(10), 3)
 print(Z)
 
+# Author: Jeff Luo (@Jeff1999)
+
+Z = np.arange(10)
+print(sliding_window_view(Z, window_shape=3))
+
 < q77
 How to negate a boolean, or to change the sign of a float inplace? (★★★)
 
@@ -1135,7 +1148,7 @@ print(R)
 Consider an array Z = [1,2,3,4,5,6,7,8,9,10,11,12,13,14], how to generate an array R = [[1,2,3,4], [2,3,4,5], [3,4,5,6], ..., [11,12,13,14]]? (★★★)
 
 < h81
-hint: stride_tricks.as_strided
+hint: stride_tricks.as_strided, from numpy.lib.stride_tricks import sliding_window_view (np>=1.20.0)
 
 < a81
 # Author: Stefan van der Walt
@@ -1144,6 +1157,11 @@ Z = np.arange(1,15,dtype=np.uint32)
 R = stride_tricks.as_strided(Z,(11,4),(4,4))
 print(R)
 
+# Author: Jeff Luo (@Jeff1999)
+
+Z = np.arange(1, 15, dtype=np.uint32)
+print(sliding_window_view(Z, window_shape=4))
+
 < q82
 Compute a matrix rank (★★★)
 
@@ -1178,7 +1196,7 @@ print(np.bincount(Z).argmax())
 Extract all the contiguous 3x3 blocks from a random 10x10 matrix (★★★)
 
 < h84
-hint: stride_tricks.as_strided
+hint: stride_tricks.as_strided, from numpy.lib.stride_tricks import sliding_window_view (np>=1.20.0)
 
 < a84
 # Author: Chris Barker
@@ -1190,6 +1208,11 @@ j = 1 + (Z.shape[1]-3)
 C = stride_tricks.as_strided(Z, shape=(i, j, n, n), strides=Z.strides + Z.strides)
 print(C)
 
+# Author: Jeff Luo (@Jeff1999)
+
+Z = np.random.randint(0,5,(10,10))
+print(sliding_window_view(Z, window_shape=(3, 3)))
+
 < q85
 Create a 2D array subclass such that Z[i,j] == Z[j,i] (★★★)
 
@@ -1238,7 +1261,7 @@ print(S)
 Consider a 16x16 array, how to get the block-sum (block size is 4x4)? (★★★)
 
 < h87
-hint: np.add.reduceat
+hint: np.add.reduceat, from numpy.lib.stride_tricks import sliding_window_view (np>=1.20.0)
 
 < a87
 # Author: Robert Kern
@@ -1258,6 +1281,12 @@ k = 4
 windows = np.lib.stride_tricks.sliding_window_view(Z, (k, k))
 S = windows[::k, ::k, ...].sum(axis=(-2, -1))
 
+# Author: Jeff Luo (@Jeff1999)
+
+Z = np.ones((16, 16))
+k = 4
+print(sliding_window_view(Z, window_shape=(k, k))[::k, ::k].sum(axis=(-2, -1)))
+
 < q88
 How to implement the Game of Life using numpy arrays? (★★★)
 
