numpy创建矩阵常用方法

numpy创建矩阵常用方法

arange+reshape

in:

n = np.arange(0, 30, 2)# start at 0 count up by 2, stop before 30
n = n.reshape(3, 5) # reshape array to be 3x5

• 1
• 2

out:

linspace+resize

in：

o = np.linspace(0, 4, 9)
o.resize(3, 3)

• 1
• 2

out:

notice:reshape与resize区别

ones zeros eye diag random.randint等创建矩阵

in：

np.ones((3, 2))
np.zeros((2, 3))
np.eye(3)#3维单位矩阵
y = np.array([4, 5, 6])
np.diag(y)#以y为主对角线创建矩阵
np.random.randint(0, 10, (4,3))

• 1
• 2
• 3
• 4
• 5
• 6

out：

ones: 
[[ 1. 1.] 
[ 1. 1.] 
[ 1. 1.]] 
zeros: 
[[ 0. 0. 0.] 
[ 0. 0. 0.]] 
eye: 
[[ 1. 0. 0.] 
[ 0. 1. 0.] 
[ 0. 0. 1.]] 
diag: 
[[4 0 0] 
[0 5 0] 
[0 0 6]] 
randint 
[[1 3 5] 
[4 4 3] 
[9 3 0] 
[7 0 0]]

矩阵拼接

in:

p = np.ones([2, 3], int)
np.hstack([p, 2*p])#水平拼接
np.vstack([p, 2*p])#竖直拼接

• 1
• 2
• 3

out:

hstack： 
[[1 1 1 2 2 2] 
[1 1 1 2 2 2]] 
vstack: 
[[1 1 1] 
[1 1 1] 
[2 2 2] 
[2 2 2]]

备注:

1 矩阵常用操作:

>>> b1 = array([[1,2,3],[4,5,6],[7,8,9]])
>>> b1[1:2]
array([[4, 5, 6]])