numpyの理解を深めるために100問エクササイズに挑戦してみました。
今回は21問目から30問目までです。
21. Create a checkerboard 8×8 matrix using the tile function.
Z = np.tile(np.array([[0,1],[1,0]]), (4,4))
print(Z)[[0 1 0 1 0 1 0 1]
[1 0 1 0 1 0 1 0]
[0 1 0 1 0 1 0 1]
[1 0 1 0 1 0 1 0]
[0 1 0 1 0 1 0 1]
[1 0 1 0 1 0 1 0]
[0 1 0 1 0 1 0 1]
[1 0 1 0 1 0 1 0]]メソッド「tile」は与えた配列をタイル状に並べてくれます。
22. Normalize a 5×5 random matrix.
Z = np.random.random((5,5))
Z = (Z - np.mean (Z)) / (np.std (Z))
print(Z)[[-1.15386639 0.25349436 -1.34700028 1.50198517 -0.87798254]
[ 0.66758545 0.69862527 1.18777135 -0.76942776 -0.86469872]
[ 0.80640373 0.87257176 -0.80934667 1.20730198 0.10682863]
[-1.34667656 -1.34467025 1.19164124 -0.27454829 -1.82187067]
[ 0.86900007 -0.64711533 0.230963 1.32989505 0.33313639]]23. Create a custom dtype that describes a color as four unsigned bytes (RGBA).
color = np.dtype([("r", np.ubyte),("g", np.ubyte),("b", np.ubyte),("a", np.ubyte)])24. Multiply a 5×3 matrix by a 3×2 matrix (real matrix product).
Z = np.dot(np.ones((5,3)), np.ones((3,2)))
print(Z)
Z = np.ones((5,3)) @ np.ones((3,2))
print(Z)[[3. 3.]
[3. 3.]
[3. 3.]
[3. 3.]
[3. 3.]]
[[3. 3.]
[3. 3.]
[3. 3.]
[3. 3.]
[3. 3.]]メソッド「dot」は行列の掛け算をしてくれます。
25. Given a 1D array, negate all elements which are between 3 and 8, in place.
Z = np.arange(11)
Z[(3 < Z) & (Z < 8)] *= -1
print(Z)[ 0 1 2 3 -4 -5 -6 -7 8 9 10]26. What is the output of the following script?
print(sum(range(5),-1))
from numpy import *
print(sum(range(5),-1))9
1027. Consider an integer vector Z, which of these expressions are legal?
Z = np.arange(5)
print(Z**Z)
print(2 << Z >> 2)
print(Z <- Z)
print(1j*Z)
print(Z/1/1)
print(Z<Z>Z)[ 1 1 4 27 256]
[0 1 2 4 8]
[False False False False False]
[0.+0.j 0.+1.j 0.+2.j 0.+3.j 0.+4.j]
[0. 1. 2. 3. 4.]
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-24-6af43e8cc83e> in <module>()
5 print(1j*Z)
6 print(Z/1/1)
----> 7 print(Z<Z>Z)
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()28. What are the result of the following expressions?
np.array(0) / np.array(0)
np.array(0) // np.array(0)
np.array([np.nan]).astype(int).astype(float)/usr/local/lib/python3.7/dist-packages/ipykernel_launcher.py:1: RuntimeWarning: invalid value encountered in true_divide
"""Entry point for launching an IPython kernel.
/usr/local/lib/python3.7/dist-packages/ipykernel_launcher.py:2: RuntimeWarning: divide by zero encountered in floor_divide
array([-9.22337204e+18])29. How to round away from zero a float array?
Z = np.random.uniform(-10,+10,10)
print(np.copysign(np.ceil(np.abs(Z)), Z))[ 8. -9. -10. 8. 5. 2. 4. 9. 7. 3.]30. How to find common values between two arrays?
Z1 = np.random.randint(0,10,10)
Z2 = np.random.randint(0,10,10)
print(np.intersect1d(Z1,Z2))[0 6 7 8]次回は31〜40問目に挑戦してみます。