Python reduce()

Description

The reduce(fun,seq) function is used to apply a particular function passed in its argument to all of the list elements mentioned in the sequence passed along.This function is defined in “functools” module.

Working : 

• At first step, first two elements of sequence are picked and the result is obtained.
• Next step is to apply the same function to the previously attained result and the number just succeeding the second element and the result is again stored.
• This process continues till no more elements are left in the container.
• The final returned result is returned and printed on console.

reduce() 函数会对参数序列中元素进行累积。

函数将一个数据集合（链表，元组等）中的所有数据进行下列操作：用传给 reduce 中的函数 function（有两个参数）先对集合中的第 1、2 个元素进行操作，得到的结果再与第三个数据用 function 函数运算，最后得到一个结果。

Example

# python code to demonstrate working of reduce()

  

# importing functools for reduce()

import functools

  

# initializing list

lis = [ 1 , 3, 5, 6, 2, ]

  

# using reduce to compute sum of list

print ("The sum of the list elements is : ",end="")

print (functools.reduce(lambda a,b : a+b,lis))

  

# using reduce to compute maximum element from list

print ("The maximum element of the list is : ",end="")

print (functools.reduce(lambda a,b : a if a > b else b,lis))

 

 

Output:

The sum of the list elements is : 17
The maximum element of the list is : 6

Detail

Using Operator Functions

reduce() can also be combined with operator functions to achieve the similar functionality as with lambda functions and makes the code more readable.

# python code to demonstrate working of reduce()

# using operator functions

  

# importing functools for reduce()

import functools

  

# importing operator for operator functions

import operator

  

# initializing list

lis = [ 1 , 3, 5, 6, 2, ]

  

# using reduce to compute sum of list

# using operator functions

print ("The sum of the list elements is : ",end="")

print (functools.reduce(operator.add,lis))

  

# using reduce to compute product

# using operator functions

print ("The product of list elements is : ",end="")

print (functools.reduce(operator.mul,lis))

  

# using reduce to concatenate string

print ("The concatenated product is : ",end="")

print (functools.reduce(operator.add,["holy","fucking","shit"]))

Output

The sum of the list elements is : 17
The product of list elements is : 180
The concatenated product is : holyfuckingshit

reduce() vs accumulate() 

Both reduce() and accumulate() can be used to calculate the summation of a sequence elements. But there are differences in the implementation aspects in both of these.

• reduce() is defined in “functools” module, accumulate() in “itertools” module.
• reduce() stores the intermediate result and only returns the final summation value. Whereas, accumulate() returns a iterator containing the intermediate results. The last number of the iterator returned is summation value of the list.
• reduce(fun,seq) takes function as 1st and sequence as 2nd argument. In contrast accumulate(seq,fun) takes sequence as 1st argument and function as 2nd argument.

# python code to demonstrate summation 

# using reduce() and accumulate()

  

# importing itertools for accumulate()

import itertools

  

# importing functools for reduce()

import functools

  

# initializing list 

lis = [ 1, 3, 4, 10, 4 ]

  

# priting summation using accumulate()

print ("The summation of list using accumulate is :",end="")

print (list(itertools.accumulate(lis,lambda x,y : x+y)))

  

# priting summation using reduce()

print ("The summation of list using reduce is :",end="")

print (functools.reduce(lambda x,y:x+y,lis))

Output:

The summation of list using accumulate is :[1, 4, 8, 18, 22]
The summation of list using reduce is :22