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

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]

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)**.

`# 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` `output ` ` ` `else` `: ` ` ` `print` `'No Common Elements Found'` |

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*filter_none*

Output:

Common Elements = [2,3]

This article is contributed by **Shashank Mishra (Gullu)**. 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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