对List进行排序,Python提供了两个方法
list.sort(func=None, key=None, reverse=False)
Python实例:
>>> list = [2,5,8,9,3]
>>> list
[2,5,8,9,3]
>>> list.sort()
>>> list
[2, 3, 5, 8, 9]
Python实例:
>>> list = [2,5,8,9,3]
>>> list
[2,5,8,9,3]
>>> sorted(list)
[2, 3, 5, 8, 9]
实例1:正向排序:
>>>L = [2,3,1,4] >>>L.sort() >>>L >>>[1,2,3,4]
实例2:反向排序:
>>>L = [2,3,1,4]
>>>L.sort(reverse=True)
>>>L
[4,3,2,1]
实例3:对第二个关键字排序:
>>>L = [('b',6),('a',1),('c',3),('d',4)]
>>>L.sort(lambda x,y:cmp(x[1],y[1]))
>>>L
[('a', 1), ('c', 3), ('d', 4), ('b', 6)]
实例4: 对第二个关键字排序:
>>>L = [('b',6),('a',1),('c',3),('d',4)]
>>>L.sort(key=lambda x:x[1])
>>>L
[('a', 1), ('c', 3), ('d', 4), ('b', 6)]
实例5: 对第二个关键字排序:
>>>L = [('b',2),('a',1),('c',3),('d',4)]
>>>import operator
>>>L.sort(key=operator.itemgetter(1))
>>>L
[('a', 1), ('b', 2), ('c', 3), ('d', 4)]
实例6:(DSU方法:Decorate-Sort-Undercorate):
>>>L = [('b',2),('a',1),('c',3),('d',4)]
>>>A = [(x[1],i,x) for i,x in enumerate(L)] #i can confirm the stable sort
>>>A.sort()
>>>L = [s[2] for s in A]
>>>L
[('a', 1), ('b', 2), ('c', 3), ('d', 4)]
以上给出了6中对List排序的方法,其中实例3.4.5.6能起到对以List item中的某一项
为比较关键字进行排序.
效率比较:
cmp < DSU < key
通过实验比较,方法3比方法6要慢,方法6比方法4要慢,方法4和方法5基本相当 。
实例7:
>>>L = [('d',2),('a',4),('b',3),('c',2)]
>>> L.sort(key=lambda x:x[1])
>>> L
[('d', 2), ('c', 2), ('b', 3), ('a', 4)]
我们看到,此时排序过的L是仅仅按照第二个关键字来排的,
如果我们想用第二个关键字排过序后再用第一个关键字进行排序呢?有两种方法 :
实例8:
>>> L = [('d',2),('a',4),('b',3),('c',2)]
>>> L.sort(key=lambda x:(x[1],x[0]))
>>> L
[('c', 2), ('d', 2), ('b', 3), ('a', 4)]
实例9:
>>> L = [('d',2),('a',4),('b',3),('c',2)]
>>> L.sort(key=operator.itemgetter(1,0))
>>> L
[('c', 2), ('d', 2), ('b', 3), ('a', 4)]