python中几个常用高阶函数

import collections
from functools import reduce
from itertools import groupby

# 计数
li = ['sunxiaohui', 'zhangzh', 'sunxiaohui', 'sunxiaohui']
counter = collections.Counter(li)
print(counter)  # Counter({'sunxiaohui': 3, 'zhangzh': 1})

# 每一个key默认都是list
obj = collections.defaultdict(list)
print(obj['abc'])  # []

print("*" * 80)

ll = [1, 2, 3, 4]

# map 映射每一个元素
result = map(lambda x: x * 2, ll)
print(list(result))  # [2, 4, 6, 8]

# reduce 合并两个元素
result2 = reduce(lambda x, y: x + y, ll)
print(result2)  # 10

# filter 只返回True结果
result3 = filter(lambda x: x % 2 == 0, ll)
print(list(result3))  # [2, 4]

list_data = [
    {"id": 101, "title": "标题1", "categroy": "python"},
    {"id": 102, "title": "标题2", "categroy": "java"},
    {"id": 103, "title": "标题3", "categroy": "js"},
    {"id": 104, "title": "标题4", "categroy": "java"},
    {"id": 105, "title": "标题5", "categroy": "go"},
    {"id": 106, "title": "标题6", "categroy": "rust"},
    {"id": 107, "title": "标题7", "categroy": "python"},
    {"id": 108, "title": "标题8", "categroy": "js"},
    {"id": 109, "title": "标题9", "categroy": "python"},
    {"id": 110, "title": "标题10", "categroy": "java"},
]

arr = sorted(list_data, key=lambda x: x['categroy'])
# for v in arr:
#     print(v)

result4 = groupby(arr, key=lambda x: x['categroy'])
# print(list(result4))

for key, value in result4:
    print(key, list(value))

# go [{'id': 105, 'title': '标题5', 'categroy': 'go'}]
# java [{'id': 102, 'title': '标题2', 'categroy': 'java'}, {'id': 104, 'title': '标题4', 'categroy': 'java'}, {'id': 110, 'title': '标题10', 'categroy': 'java'}]
# js [{'id': 103, 'title': '标题3', 'categroy': 'js'}, {'id': 108, 'title': '标题8', 'categroy': 'js'}]
# python [{'id': 101, 'title': '标题1', 'categroy': 'python'}, {'id': 107, 'title': '标题7', 'categroy': 'python'}, {'id': 109, 'title': '标题9', 'categroy': 'python'}]
# rust [{'id': 106, 'title': '标题6', 'categroy': 'rust'}]