代码示例：

data = [
    {'name': 'Alice', 'age': 25, 'city': 'New York'},
    {'name': 'Bob', 'age': 30, 'city': 'Los Angeles'},
    {'name': 'Charlie', 'age': 35, 'city': 'San Francisco'},
    {'name': 'David', 'age': 40, 'city': 'New York'},
    {'name': 'Emma', 'age': 45, 'city': 'San Francisco'}
]

# Group by the city and filter on age greater than 30
result = {}
for item in data:
    if item['city'] not in result:
        result[item['city']] = []
    if item['age'] > 30:
        result[item['city']].append(item)
print(result)

输出结果：

{'New York': [{'name': 'David', 'age': 40, 'city': 'New York'}], 'Los Angeles': [], 'San Francisco': [{'name': 'Charlie', 'age': 35, 'city': 'San Francisco'}, {'name': 'Emma', 'age': 45, 'city': 'San Francisco'}]}