pythonmap和list_python中map()与zip()操作方法

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:

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:

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)]

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:

[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:

[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:

[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]