2.6 比较、掩码和布尔逻辑

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本文源码请见我的GitHub

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import pandas as pd
import numpy as np
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rainfall = pd.read_csv('./Seattle2014.csv')
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rainfall =rainfall['PRCP'].values
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inches = rainfall / 254 #1/1mm ->inches
inches.shape
(365,)

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%matplotlib inline
import matplotlib.pyplot as plt
import seaborn as sns; sns.set()
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plt.hist(inches, 40);

2.6.2 和通用函数类似的比较操作

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x = np.array([1, 2, 3, 4, 5])
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x < 3
array([ True,  True, False, False, False])

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x > 3
array([False, False, False,  True,  True])

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x <= 3
array([ True,  True,  True, False, False])

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x!=3
array([ True,  True, False,  True,  True])

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x == 3
array([False, False,  True, False, False])

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(2 * x)  == (x ** 2)
array([False,  True, False, False, False])

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rng = np.random.RandomState(0)
x = rng.randint(10, size = (3, 4))
x
array([[5, 0, 3, 3],
       [7, 9, 3, 5],
       [2, 4, 7, 6]])

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x < 6
array([[ True,  True,  True,  True],
       [False, False,  True,  True],
       [ True,  True, False, False]])

2.6.3 布尔数组

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print(x)
[[5 0 3 3]
 [7 9 3 5]
 [2 4 7 6]]

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np.count_nonzero(x < 6)
8

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np.sum(x < 6)
8

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np.sum(x < 6, axis=1)
array([4, 2, 2])

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np.any(x > 8)
True

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np.any(x < 0)
False

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np.all(x < 10)
True

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np.all(x == 6)
False

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np.all(x < 8, axis = 1)
array([ True, False,  True])

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np.sum((inches > 0.5) | (inches >= 1))
37

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print("number days without rain: ",np.sum(inches == 0))
print("number days with rain",np.sum(inches!=0))
print("days with more than 0.5 inches:",np.sum(inches > 0.5))
number days without rain:  215
number days with rain 150
days with more than 0.5 inches: 37

2.6.4 江布尔数组作为掩码

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x
array([[5, 0, 3, 3],
       [7, 9, 3, 5],
       [2, 4, 7, 6]])

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x < 5
array([[False,  True,  True,  True],
       [False, False,  True, False],
       [ True,  True, False, False]])

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x[x<5]
array([0, 3, 3, 3, 2, 4])