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

  • Last Updated : 23 Nov, 2020

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


Input :  arr = [[1,2,3,4],
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:]: 
    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) 
        print ('No Common Elements Found')


Common Elements = [2,3]

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