cs231n-svm-note

import numpy as np

range 的用法

list(range(1,5))

[1, 2, 3, 4]

list(range(5))

[0, 1, 2, 3, 4]

np.random.choice 的用法·

mask = np.random.choice(100,10)
mask

array([78, 69, 24, 91, 24, 65, 16, 22, 80, 53])

rangrange 的用法

from random import randrange

randrange(5) # 随机取一个数字，不包含 endpoint

2

randrange(2,5)

2

[randrange(i) for i in (500,3073)]

[65, 39]

数组索引的一种方式

a = np.array([[1,2,3],[4,5,6],[7,8,9]])
a[(1,2)]

6

np.max((0,-1))

0

a = np.array([[1,2,3],[4,5,6],[7,8,9]])
x = a[(1,1,2),(2,1,0)]
x

array([6, 5, 7])

np.sum(a,axis=0)

array([12, 15, 18])

a = np.array([[1,2,3],[4,5,6],[7,8,9]])
a[(1,1,2),(2,1,0)] = a[(1,1,2),(2,1,0)] - np.array([0,1,2])
a

array([[1, 2, 3],
       [4, 4, 6],
       [5, 8, 9]])

a[1,:]

array([4, 4, 6])

import copy

copy.copy() 是浅拷贝，只拷贝父对象，不会拷贝父对象的子对象
copy.deepcopy() 深拷贝，拷贝父对象及其子对象

a = [1,2,3,4,['a','b']]
b = copy.copy(a)
c = copy.deepcopy(a)
d = a
a.append(5)
a[4].append('c')
print('a=', a)
print('b=', b)
print('c=', c)
print('d=', d)

a= [1, 2, 3, 4, ['a', 'b', 'c'], 5]
b= [1, 2, 3, 4, ['a', 'b', 'c']]
c= [1, 2, 3, 4, ['a', 'b']]
d= [1, 2, 3, 4, ['a', 'b', 'c'], 5]