索引和切片（下）

• 花式索引

import numpy as np

data2=[[8.5,6,4.1,2,0.7],[1.5,3,5.4,7,3.9],[3.2,4.5,6,3,9]]
arr2=np.array(data2)
# array([[8.5, 6. , 4.1, 2. , 0.7],
         [1.5, 3. , 5.4, 7. , 3.9],
         [3.2, 4.5, 6. , 3. , 9. ]])

arr2[[2,1]]  
# array([[3.2, 4.5, 6. , 3. , 9. ],
       [1.5, 3. , 5.4, 7. , 3.9]])

arr2[[2,2],[0,1]]  # arr2[2,0]  arr2[2,1]
# array([3.2, 4.5])

arr2[:,[3,1]]
array([[2. , 6. ],
       [7. , 3. ],
       [3. , 4.5]])

arr2[:,1]
# array([6. , 3. , 4.5])

arr2[:,[1]]

# array([[6. ],
        [3. ],
        [4.5]])

arr2[np.ix_([0,-1],[0,1,3])]
# array([[8.5, 6. , 2. ], 
         [3.2, 4.5, 3. ]])

arr2[[0,-1]]
# array([[8.5, 6. , 4.1, 2. , 0.7],
         [3.2, 4.5, 6. , 3. , 9. ]])
arr2[[0,-1]][:,[0,1,3]]
# array([[8.5, 6. , 2. ],
         [3.2, 4.5, 3. ]])