按JSON键分组对象列表

import json
from collections import defaultdict

# 示例数据
data = [
    {"name": "Alice", "age": 25, "city": "New York"},
    {"name": "Bob", "age": 30, "city": "Los Angeles"},
    {"name": "Charlie", "age": 25, "city": "New York"},
    {"name": "David", "age": 30, "city": "Chicago"}
]

# 按照年龄分组
grouped_by_age = defaultdict(list)
for item in data:
    grouped_by_age[item["age"]].append(item)

# 转换为JSON格式
json_result = json.dumps(grouped_by_age, indent=4)
print(json_result)

{
    "25": [
        {
            "name": "Alice",
            "age": 25,
            "city": "New York"
        },
        {
            "name": "Charlie",
            "age": 25,
            "city": "New York"
        }
    ],
    "30": [
        {
            "name": "Bob",
            "age": 30,
            "city": "Los Angeles"
        },
        {
            "name": "David",
            "age": 30,
            "city": "Chicago"
        }
    ]
}

if "age" in item:
    grouped_by_age[item["age"]].append(item)

grouped_by_age[item.get("age", "unknown")].append(item)

for item in data:
    age = item.get("age", "unknown")
    grouped_by_age[age].append(item)