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Without converting Numpy arrays to sets, what is the approach to find the set intersection of two or more Numpy arrays or lists?

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You can use the intersect1d() function of Numpy that returns the sorted, unique elements that are in both of the input Numpy arrays or lists. Here is an example:

>>> import numpy as np
>>> a=np.array([11,12,13,14,15])
>>> b=np.array([14,15,16,17,18])
>>> np.intersect1d(a,b)
array([14, 15])

If you want to find the set intersection of more than two arrays, you need to use the reduce() function of functools or the intersect1d() function recursively. Here is an example:

>>> from functools import reduce
>>> c=np.array([14,15,17,18,19,21,20])
>>> reduce(np.intersect1d,(a,b,c))
array([14, 15])

>>> np.intersect1d(np.intersect1d(a,b),c)
array([14, 15])