numpy学习笔记

import numpy as np


alone_array=np.array([12,23,34,45,56,77])

alone_array2=np.array([12,23,34,45,56,77])

print(alone_array.dot(alone_array2))
n_array=np.array([[1,2,3],[4,5,6],[7,8,9]])
print(n_array.sort())
z_array=np.zeros((3,3))
o_array=np.ones((4,4))
e_array=np.empty((2,3),dtype="int32")
a_array=np.arange(1,20,5)
str_array=np.array(["1","2","3"])
arr2d=np.array([[2,3,33,2,5],[2,2,3,1,12],
                [2,3,6,6,5],[5,55,6,33,23],
                [33,6,43,7,3]
                ])

print(z_array.shape,z_array.ndim,a_array,e_array.dtype.name)

# 类型转换
e_array=e_array.astype(np.float32)
str_array=str_array.astype(np.int64)
print(e_array.dtype.name)

# 索引读取
print(arr2d[0],arr2d[1,0],arr2d[1:],arr2d[:2,:2],arr2d[:,2])
# 花式索引
print(alone_array[[1,4,3]])
print(arr2d[[1,4]])
print(arr2d[[1,4],[2,3]])

# 数组重塑
new_2darr=arr2d.reshape(3,3)
print(new_2darr)

# 数组重塑
array_1d=np.arange(1,13)
array_2d=array_1d.reshape((6,2))
print(array_2d.shape)
new_array_2d=array_2d.reshape((3,4))

# 数组转置
arr=np.arange(24).reshape((2,3,4))
print(arr)
new_arr=arr.transpose((0,1,2))
print(new_arr)

# where函数
arr_x=np.array(1,5,7)
arr_con=np.array([True,False,True])

# 唯一值
arr=np.array([12,23,34,45,56,77])
np.unique(arr)