本文介绍对Python字典的按键和按值排序的几种方式。
按键排序# 对字典按键排序
def sort_by_key(d):
'''
d.items() 返回元素为 (key, value) 的可迭代类型(Iterable),
key 函数的参数 k 便是元素 (key, value),所以 k[0] 取到字典的键。
'''
return sorted(d.items(), key=lambda k: k[0])
def main():
dic = {'a': 2018, 'z': 2019, 'b': 2017}
print(sorted(dic)) # ['a', 'b', 'z']
print(sort_by_key(dic)) # [('a', 2018), ('b', 2017), ('z', 2019)]
print(dict(sort_by_key(dic))) # {'a': 2018, 'b': 2017, 'z': 2019}
if __name__ == '__main__':
main()
如上所示:
- 如果直接调用
sorted
函数,只会对字典的键进行排序,返回键排序后的列表['a', 'b', 'z']
- 通过自己编写
sort_by_key
函数,首先通过sorted
函数返回列表,然后其中包含的元素为 tuple:('a', 2018), ('b', 2017), ('z', 2019)
- 如果想得到按键排序后的字典,可以通过
dict
函数将包含元组的列表转换为所需要的字典{'a': 2018, 'b': 2017, 'z': 2019}
同理,如果我们只需要对sort_by_value稍微修改一下,就可以得到按值排序的结果:
def sort_by_value(d):
return sorted(d.items(), key=lambda k: k[1]) # k[1] 取到字典的值。
def main():
dic = {'a': 2018, 'z': 2019, 'b': 2017}
print(sort_by_value(dic)) # [('b', 2017), ('a', 2018), ('z', 2019)]
if __name__ == '__main__':
main()
collections模块的OrderedDict
from collections import OrderedDict
sort_dict_by_key = OrderedDict(dic) # 默认按键排序
print(sorted_dict_by_key) # OrderedDict([('a', 2018), ('z', 2019), ('b', 2017)])
sort_dict_by_value = OrderedDict(sorted(dic.items(), key=lambda k: k[1]))
print(sort_dict_by_value) # OrderedDict([('b', 2017), ('a', 2018), ('z', 2019)])
operator模块
from operator import itemgetter
dic = {'a': 2018, 'z': 2019, 'b': 2017}
print('Original dictionary : ', dic)
sorted_d = dict(sorted(dic.items(), key=itemgetter(0)))
print('Dictionary in ascending order by key : ', sorted_d)
sorted_d = dict(sorted(dic.items(), key=itemgetter(1)))
print('Dictionary in ascending order by value : ', sorted_d)
结果:
Original dictionary : {'a': 2018, 'z': 2019, 'b': 2017}
Dictionary in ascending order by key : {'a': 2018, 'b': 2017, 'z': 2019}
Dictionary in ascending order by value : {'b': 2017, 'a': 2018, 'z': 2019}