exercises.py

# http://www.scipy-lectures.org/intro/numpy/exercises.html

import numpy as np
# 1
a = np.linspace(1,15,15).reshape([3,5]).T
b = a[[1,3],:]

# 2
a = np.arange(25).reshape(5, 5)
b = np.array([1., 5, 10, 15, 20])
# array([  1.,   5.,  10.,  15.,  20.])
# shape: (5,)

# b[:,np.newaxis] =
# array([[  1.],
#        [  5.],
#        [ 10.],
#        [ 15.],
#        [ 20.]])
# shape: (5, 1)
c = a/b[:,np.newaxis]

# 3
a = np.random.random([10,3])
# array([[ 0.09583662,  0.68293089,  0.08176245],
#        [ 0.5044622 ,  0.89548375,  0.586283  ],
#        [ 0.14241036,  0.94341594,  0.80657279],
#        [ 0.70212222,  0.79018404,  0.43425573],
#        [ 0.73331918,  0.79883131,  0.66549872],
#        [ 0.7642978 ,  0.01023381,  0.96184134],
#        [ 0.77596693,  0.73808234,  0.95999951],
#        [ 0.92064225,  0.39235637,  0.65809024],
#        [ 0.17385709,  0.75346265,  0.99849483],
#        [ 0.65049734,  0.58286805,  0.57900828]])
b = np.abs(a-0.5)
# array([[ 0.40416338,  0.18293089,  0.41823755],
#        [ 0.0044622 ,  0.39548375,  0.086283  ],
#        [ 0.35758964,  0.44341594,  0.30657279],
#        [ 0.20212222,  0.29018404,  0.06574427],
#        [ 0.23331918,  0.29883131,  0.16549872],
#        [ 0.2642978 ,  0.48976619,  0.46184134],
#        [ 0.27596693,  0.23808234,  0.45999951],
#        [ 0.42064225,  0.10764363,  0.15809024],
#        [ 0.32614291,  0.25346265,  0.49849483],
#        [ 0.15049734,  0.08286805,  0.07900828]])
c = np.argsort(b)
# 有问题，排序不对
# array([[1, 0, 2],
#        [0, 2, 1],
#        [2, 0, 1],?
#        [2, 0, 1],?
#        [2, 0, 1],?
#        [0, 2, 1],
#        [1, 0, 2],
#        [1, 2, 0],?
#        [1, 0, 2],
#        [2, 1, 0]])
a[c==0]