np.newaxis的作用就是在这一位置增加一个维度，这一位置指的是np.newaxis所在的位置
x1 = np.array([1, 2, 3, 4, 5]) # the shape of x1 is (5,)
这里x1的shape为(5,) ,这里我们用newaxis，改变维度
x1_new = x1[:, np.newaxis] # now, the shape of x1_new is (5, 1) # array([[1], # [2], # [3], # [4], # [5]]) x1_new = x1[np.newaxis,:] # now, the shape of x1_new is (1, 5) # array([[1, 2, 3, 4, 5]])
接着往外引申一下：
# promoting 1D array to a 3D array x1_3D = x1[np.newaxis,：, np.newaxis] x1_3D.shape #(1, 5, 1)
同时我改变维度还可以用另一个方法:
shape
x1.shape = (5,1) # now, the shape of x1 is (5, 1) # array([[1], # [2], # [3], # [4], # [5]])
