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 ?


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 output
        print 'No Common Elements Found'



Common Elements = [2,3]

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