python中map()与zip()操作方法

时间:2022-09-23 17:56:06

对于map()它的原型是:map(function,sequence),就是对序列sequence中每个元素都执行函数function操作。
比如之前的a,b,c = map(int,raw_input().split()),意思就是说把输入的a,b,c转化为整数。再比如:

?
1
2
3
a = ['1','2','3','4']
print map(list,a)
print map(int,a)

第一个map是把列表a中每个元素转化为列表,第二个map是把a中每个元素转化为整数。
而对于zip(),原型是zip(*list),list是一个列表,zip(*list)返回的是一个元组,比如:

?
1
2
3
list = [[1,2,3],[4,5,6],[7,8,9]]
t = zip(*list)
print t

输出:[(1, 4, 7), (2, 5, 8), (3, 6, 9)]

?
1
2
3
4
x = [1,2,3,4,5]
y = [6,7,8,9,10]
a = zip(x,y)
print a

输出:[(1, 6), (2, 7), (3, 8), (4, 9), (5, 10)]

下面是一些补充:

?
1
2
3
4
5
6
[python]
>>> list = [[0,1,2],[3,1,4]]
>>> [sum(x) for x in list]
[3, 8]
>>> map(sum,list)
[3, 8]

如果要得到每列之和,需要用zip(*list)先unzip list,得到一个元组list,其中第i个元组包含了每行的第i个元素:

?
1
2
3
4
5
6
7
8
[python]
>>> list = [[0,1,2],[3,1,4]]
>>> zip(*list)
[(0, 3), (1, 1), (2, 4)]
>>> [sum(x) for x in zip(*list)]
[3, 2, 6]
>>> map(sum,zip(*list))
[3, 2, 6]

下面的例子是关于zip和unzip(其实是zip和*一起用)如何work的:

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
[python]
>>> x=[1,2,3]
>>> y=[4,5,6]
>>> zipped = zip(x,y)
>>> zipped
[(1, 4), (2, 5), (3, 6)]
>>> x2,y2=zip(*zipped)
>>> x2
(1, 2, 3)
>>> y2
(4, 5, 6)
>>> x3,y3=map(list,zip(*zipped))
>>> x3
[1, 2, 3]
>>> y3
[4, 5, 6]