# intersection_update() in Python to find common elements in n arrays

• Last Updated : 21 Jul, 2022

We are given list of n number of arrays, find all common elements in given arrays ? Examples:

```Input :  arr = [[1,2,3,4],
[8,7,3,2],
[9,2,6,3],
[5,1,2,3]]
Output :  Common Elements = [2,3]```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

We can solve this problem quickly in python using intersection_update() method of Set() data structure. How intersection_update() works ?

Suppose we have two sets A and B, then A.intersection_update(B) operation updates set A with common elements in set A and B. For example, A=set([1,2,3]) and B=set([4,2,3]) now after taking A.intersection_update(B), value of set A will be [2,3]. Syntax is anySet.intersection_update(iterable).

Implementation:

## Python3

 `# Function to find common elements in n arrays``def` `commonElements(arr):``    ` `    ``# initialize result with first array as a set``    ``result ``=` `set``(arr[``0``])` `    ``# now iterate through list of arrays starting from``    ``# second array and take intersection_update() of``    ``# each array with result. Every operation will``    ``# update value of result with common values in``    ``# result set and intersected set``    ``for` `currSet ``in` `arr[``1``:]:``        ``result.intersection_update(currSet)` `    ``return` `list``(result)` `# Driver code``if` `__name__ ``=``=` `"__main__"``:``    ``arr ``=` `[[``1``,``2``,``3``,``4``], [``8``,``7``,``3``,``2``], [``9``,``2``,``6``,``3``], [``5``,``1``,``2``,``3``]]``    ``output ``=` `commonElements(arr)``    ``if` `len``(output) > ``0``:``        ``print` `(``"Common Element = "``,output)``    ``else``:``        ``print` `(``'No Common Elements Found'``)`

Output

`Common Element =  [2, 3]`

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