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from IPython.display import display_pretty
import numpy as np

indexing

common single element indexing
complex indexing
index arrays
Boolean or “mask” index arrays
Structural indexing tools
Assigning values to indexed arrays
Dealing with variable numbers of indices within programs



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a = np.arange(35).reshape(5,7)
b = a[1:5:2, ::3]
c = a[[0, 2, 4], [0, 1, 2]]
d = a[[0, 2, 4], 1]
x = np.arange(10, 0, -1)
e = x[np.array([[1, 5], [4, 6]])]
display_pretty(b ,c, d, e)

# boolean/mask indexing ways
f = x[x>5]
display_pretty(f)

g = a > 20
h = g[:, 5]
i = a[h]
display_pretty(g, h, i)

Structural indexing tools



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x = np.arange(0, 5)
y1 = x[:, np.newaxis] + x[np.newaxis, :]
x = np.arange(81).reshape([3, 3, 3, 3])
y2 = x[1, :, :, 2]
display_pretty(y1, y2)

Assigning values to indexed arrays



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x = np.arange(10, 50, 10)
x[np.array([1, 1, 3, 1])] += 1
x

Dealing with variable numbers of indices within programs



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x = np.arange(81).reshape([3, 3, 3, 3])
y1 = x[1, 1, 1, 1]
y2 = x[[1, 1, 1, 1]]
display_pretty(y1, y2)