import numpy as np
a = np.array([1, 2])
b = np.array([3, 4])
c = np.vstack((a, b))
print(c.shape)

import numpy as np
a = np.array([1, 2])
b = np.array([3, 4])
c = np.dstack((a, b))
print(c.shape)

import numpy as np 
a = np.arange(4)
x = np.hsplit(a, 2)[0]
print(x.sum())

import numpy as np
a = np.arange(6)
a = a.reshape(-1, 1)
x = np.vsplit(a, 2)[-1].sum()
print(x)

import numpy as np
a = np.arange(8).reshape((2, 2, 2))
x = np.dsplit(a, 2)[0].sum()
print(x)

import numpy as np
a = np.array([1, 2, 3, 4, 5])
b = a[[0, 1, 2]]
c = a[0:3]
b[0] = -1
c[1] = -1
print(a[0], a[1])

import numpy as np
a = np.array([[1, 3], [5, 7]])
a[:, 0] = 0
a[1, :] = 1
print(a.sum())

import numpy as np
a = np.arange(6).reshape(3, 2)
ia = np.array(((0, 0), (0, 1)))
ja = np.array(((1, 0), (0, 0)))
b = a[ia, ja]
print(b.sum() + b.ndim + b.size)

import numpy as np
a = np.array([3, 1, 2])
ia = np.array([True, False, True])
print(a[ia].sum())