从多维数组中选择由索引矩阵指定的Numpy选择矩阵

import numpy as np

# 创建一个3x3的多维数组
arr = np.array([[1, 2, 3],
                [4, 5, 6],
                [7, 8, 9]])

# 创建一个布尔索引矩阵
bool_index = arr > 4

# 使用布尔索引选择元素
selected_elements = arr[bool_index]
print("Selected elements using boolean indexing:\n", selected_elements)

# 创建一个整数索引矩阵
int_index = np.array([[0, 1],
                       [1, 2]])

# 使用整数索引选择子数组
selected_subarray = arr[int_index[:, 0], int_index[:, 1]]
print("Selected subarray using integer indexing:\n", selected_subarray)

# 错误的索引示例
try:
    invalid_index = arr[3, 3]
except IndexError as e:
    print(f"Error: {e}")

# 正确的做法
valid_index = arr[2, 2]  # 最后一个元素

# 错误的布尔索引示例
try:
    wrong_bool_index = arr > 5  # 形状不匹配
except ValueError as e:
    print(f"Error: {e}")

# 正确的做法
correct_bool_index = arr > 3  # 形状匹配