2018-01-03@望京

排序，立即想到用Python的內置函數sorted()

Python 2.x 中

sorted(...)

sorted(iterable, cmp=None, key=None, reverse=False) --> new sorted list

Python 3.x 中

sorted(iterable, key=None, reverse=False)

Return a new list containing all items from the iterable in ascending order.

A custom key function can be supplied to customise the sort order, and the

reverse flag can be set to request the result in descending order.

字典按key排序

>>> dic = {'a':9, 'c':3, 'f':12, 'b':1, 'd':7}

>>>

>>> sorted(dic)

['a', 'b', 'c', 'd', 'f']

>>>

>>> sorted(dic.keys())

['a', 'b', 'c', 'd', 'f']

>>>

>>> sorted(dic.values())

[1, 3, 7, 9, 12]

>>>

>>> sorted(dic.items())

[('a', 9), ('b', 1), ('c', 3), ('d', 7), ('f', 12)]

>>>

>>> for k in sorted(dic):

... print dic[k]

...

9

1

3

7

12

>>>

字典是無序的，對字典排序本身是一個沒有太大意義的事，但是面試的時候總會遇到==''

那么問題來了，如何對字典按照value排序呢(默認是對key進行排序)？

首先需要知道sorted()這個函數的幾個參數的意思(按照Python 3.x來說明)：

- iterable? ?指的是可迭代對象，可以是dic，dic.items()， dic.keys()，? dic.values() 等等；

- key? ? ? ? ?key對應一個函數，用來選取參與比較的元素；

-?reverse? ?排序規則. reverse = True 或者 reverse = False(默認值)；

Py2中使用sort的cmp參數自定義排序方式

>>>

>>> res = [{'name':'hi','age':10},{'name':None,'age':10},{'name':'bo','age':10},{'name':'aaa','age':10}]

>>>

>>> res.sort(cmp=lambda x, y: cmp(x['name'], y['name']))

>>>

>>> res

[{'age': 10, 'name': None}, {'age': 10, 'name': 'aaa'}, {'age': 10, 'name': 'bo'}, {'age': 10, 'name': 'hi'}]

>>>

使用key參數來實現

items()方法將字典的元素 轉化為了元組

>>> dic

{'a': 9, 'c': 3, 'b': 1, 'd': 7, 'f': 12}

>>> dic.items()

[('a', 9), ('c', 3), ('b', 1), ('d', 7), ('f', 12)]

>>>

>>> sorted(dic.items())

[('a', 9), ('b', 1), ('c', 3), ('d', 7), ('f', 12)]

>>>

>>> sorted(dic.items(), key=lambda x:x[1])

[('b', 1), ('c', 3), ('d', 7), ('a', 9), ('f', 12)]

>>>

使用zip來實現

>>> dic

{'a': 9, 'c': 3, 'b': 1, 'd': 7, 'f': 12}

>>>

>>> new_dic = zip(dic.values(), dic.keys())

>>>

>>> new_dic

[(9, 'a'), (3, 'c'), (1, 'b'), (7, 'd'), (12, 'f')]

>>>

>>> sorted(new_dic)

[(1, 'b'), (3, 'c'), (7, 'd'), (9, 'a'), (12, 'f')]

>>>