reshape(-1,3) python code example

Example: convert np shape (a,) to (a,1)

# numpy array/vector (n,) dimension -> (n,1) dimension conversion
a  = np.arange(3)         # a.shape  = (3,)
b  = a.reshape((3,1))     # b.shape  = (3,1)
c  = b.reshape((3,))      # c.shape  = (3,)

c2 = b.reshape((-1,1))    # c2.shape = (3,)