Numpy中的数组、行/列向量及其之间的转化

1.array数组

[In] import numpy as np
[In] a = np.array([1,2,3]) #一个[]对应的是既不是行向量也不是列向量，而是一个数组。
[Out] array([1, 2, 3])
[In] a.shape
[Out] (3,)
[In] b = a.T
[In] b
[Out] array([1, 2, 3])  #数组的转置仍为该数组，可见a并非是一个向量
[In] b.shape
[Out] (3,)

2. 行向量

[In] import numpy as np
	 v_r = np.array([[1,2,3]]) #2个[]对应的才是向量
	 v_r
[Out] array([[1, 2, 3]]) 
[In] v_r.shape
[Out] (1,3) 
[In] v_r.T   #将行向量转换成列向量
[Out] array([[1],
       		 [2],
             [3]]) 
[In] v_r.T.shape
[Out] (3, 1)

3.列向量

[In] v_c = np.array([[4],
                [5],
                [6]])
	 v_c
[Out] array([[4],
         	 [5],
      		 [6]])
[In] v_c.shape
[Out] (3, 1)
[In] v_c.T
[Out] array([[4, 5, 6]])
[In] v_c.T.shape
[Out] (1, 3)

4.向量和数组之间的相互转换

[In] a = np.array([7,8,9])
	 v_r = a.reshape(1,-1)   #将数组a转化为行向量
	 print(v_r)
[Out] array([[7, 8, 9]])	 
[In] v_r.shape
[Out] (1, 3)
[In] a = np.array([7,8,9])
	 v_c = a.reshape(-1,1)   #将数组a转化为行向量
	 print(v_c)
[Out] array([[7],
       		 [8],
       		 [9]])
[In] v_c.shape
[Out] (1, 3)
[In] v_r.reshape(-1)  #将行向量转化为array数组
[Out] array([7, 8, 9])
[In] v_c.reshape(-1)  #将列向量转化为array数组
[Out] array([7, 8, 9])