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reduce() in Python
• Difficulty Level : Medium
• Last Updated : 31 Mar, 2020

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.
 `# 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
```

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,[``"geeks"``,``"for"``,``"geeks"``]))`

Output

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

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
```

This article is contributed by Manjeet Singh(S.Nandini). If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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