How to use map and reduce functions in python
This article mainly shows you "python how to use map, reduce function", the content is easy to understand, clear, hope to help you solve doubts, the following let Xiaobian lead you to study and learn "python how to use map, reduce function" this article.
Format:
Map (function, list)
Reduce (function, list)
Difference:
1.map acts on each element of list and returns a new list
2.reduce integrates each element of list and returns a new value
Advantages:
1.map and reduce have their own for loop, which reduces the amount of code.
I. the use of map
#! / usr/bin/python
Def f (x):
Return Xerox
Lis = [1,2,3,4,5]
Map_list = map (f, lis) # calculate the elements of lis in the f () function respectively
Print lis
Print map_list
# str
Map_list1 = map (str, lis); # converts the elements of lis to char types in the str function
Print lis
Print map_list1
II. The use of reduce
Def fsum (x, y):
Return Xeroy
Lis = [1,3,5,7]
Lis1 = reduce (fsum, lis)
Print lis1
3. Mixed use of map / reduce
Def fsum (x, y):
Return Xeroy
Lis = [1,3,5,7]
Lis1 = reduce (fsum, lis)
Print lis1
# get numbers and
Def fadd (x, y):
Return Xerox 10
Num = reduce (fadd, lis)
Print 'get num:', num
Stri = str (num)
Print 'num2str:', stri
# convert str to digital
Def ch3num (s):
Return {'0percent: 1,' 2percent: 2, '3percent: 3,' 4percent: 4, '5percent: 5,' 6percent: 6, '7percent: 7,' 8percent: 8, '9percent: 9} [s] # this function returns as follows:
# {stri: 1, 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9} [stri [0]]-> return 1
# {stri: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9} [stri [1]]-> return 3
# {stri: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9} [stri [2]]-> return 5
# {stri: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9} [stri [4]]-- > return 7
Lis= map (ch3num, stri)
Print 'str2num:',lis
# integrate numeric list lis
Def f (XBI y):
Return Xerox 10
Num = reduce (f, strin)
Print 'add:', num
IV. Recording of difficulties
Unable to solve the problem for the time being, record it first, wait until you go deep and then look back
The function to organize it into a str2int is:
Def str2int (s):
Def fn (x, y):
Return x * 10 + y
Def char2num (s):
Return {'0: 0,'1: 1,'2,'3: 3,'4: 4,'5: 5,'6: 6,'7: 7,'8: 8,'9: 9} [s]
Return reduce (fn, map (char2num, s))
Lis = ['1mm,' 2pm,'3']
Num = str2int (lis)
Print num
Running result: 123
You can also use the lambda function to further simplify to:
Def char2num (s): return {'0: 0,'1: 1,'2: 2, 3: 3,'4: 4, 5: 5, 6: 6,'7: 7, 8: 8,'9: 9} [s] def str2int (s): return reduce (lambda x-ray: X-ray: X-ray, map (char2num, s)) lis = [1-month, 2' '4'] num = str2int (lis) print num
Running result: 124
These are all the contents of the article "how python uses map and reduce functions". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!
