对数组做基本的算术运算,将会对整个数组的所有元组进行逐一运算,并将运算结果保存在一个新的数组内,而不会破坏原始的数组
import numpy as np
a = np.array([20,40,50,80])
b = np.arange(4)
print(a)
print(b)
[20 40 50 80]
[0 1 2 3]
c = a - b
c
array([20, 39, 48, 77])
b**2 # 每个元素进行平方
array([0, 1, 4, 9], dtype=int32)
10*np.sin(a)
array([ 9.12945251, 7.4511316 , -2.62374854, -9.93888654])
a < 40
array([ True, False, False, False])
a[a>45]
array([50, 80])
A = np.array( [[1,1],
[0,1]])
B = np.array( [[2,0],
[3,4]])
print(A)
B
[[1 1]
[0 1]]
array([[2, 0],
[3, 4]])
print(A - B)
A*B
[[-1 1]
[-3 -3]]
array([[2, 0],
[0, 4]])
A.dot(B)
array([[5, 4],
[3, 4]])
np.dot(A,B)
array([[5, 4],
[3, 4]])
A@B
array([[5, 4],
[3, 4]])
A += B
A
array([[3, 1],
[3, 5]])
A *= B
A
array([[ 6, 0],
[ 9, 20]])
A.mean()
8.75
A.max()
20
A.min()
0
c = np.array(np.arange(12).reshape(3,4))
c
array([[ 0, 1, 2, 3],
[ 4, 5, 6, 7],
[ 8, 9, 10, 11]])
c.sum(axis=1) # 行上求和
array([ 6, 22, 38])
c.mean(axis=0) # 列上求均值
array([4., 5., 6., 7.])
c.cumsum(axis=1) # 行上求累加
array([[ 0, 1, 3, 6],
[ 4, 9, 15, 22],
[ 8, 17, 27, 38]], dtype=int32)
# 排序:默认是快排,从低到高
c.sort()
c
array([[ 0, 1, 2, 3],
[ 4, 5, 6, 7],
[ 8, 9, 10, 11]])
d = np.array([[1,6,2],[6,1,3],[1,5,2]])
d
array([[1, 6, 2],
[6, 1, 3],
[1, 5, 2]])
d.sort(axis=0) # 在行index上进行排序
d
array([[1, 1, 2],
[1, 5, 2],
[6, 6, 3]])
c
array([[ 0, 1, 2, 3],
[ 4, 5, 6, 7],
[ 8, 9, 10, 11]])
np.exp(c) # 求e的指数
array([[1.00000000e+00, 2.71828183e+00, 7.38905610e+00, 2.00855369e+01],
[5.45981500e+01, 1.48413159e+02, 4.03428793e+02, 1.09663316e+03],
[2.98095799e+03, 8.10308393e+03, 2.20264658e+04, 5.98741417e+04]])
np.sqrt(c)
array([[0. , 1. , 1.41421356, 1.73205081],
[2. , 2.23606798, 2.44948974, 2.64575131],
[2.82842712, 3. , 3.16227766, 3.31662479]])
np.add(c,c) # 两个c相加
array([[ 0, 2, 4, 6],
[ 8, 10, 12, 14],
[16, 18, 20, 22]])
c * 2
array([[ 0, 2, 4, 6],
[ 8, 10, 12, 14],
[16, 18, 20, 22]])
np.argsort(c, axis=0) # 返回的是排序后的索引:axis=0 行上进行排序
# c.argsort()
array([[0, 0, 0, 0],
[1, 1, 1, 1],
[2, 2, 2, 2]], dtype=int64)
np.argsort(c, axis=1) # axis=1 : 列上进行排序
array([[0, 1, 2, 3],
[0, 1, 2, 3],
[0, 1, 2, 3]], dtype=int64)