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[Python] Set Difference of Two Arrays
source link: http://siongui.github.io/2018/03/21/python-set-difference-of-two-arrays/
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[Python] Set Difference of Two Arrays
March 21, 2018
Find the elements in one array but not in the other, i.e., set difference of two arrays. In mathematical term:
A − B = {x ∈ A and x ∉ B}
The idea is to convert the array B to the data structure of key-value pairs, i.e., hash table. The hash table in Python is built-in dictionary type. Then we check if items in array A is in the hash table. If not, append the item to the difference array, and return the difference array after finish.
The following is the implementation of above idea.
# A - B
def difference(a, b):
map = {}
for x in b:
map[x] = True
diff = []
for x in a:
if x not in map:
diff.append(x)
return diff
if __name__ == "__main__":
a = [1, 2, 3, 4, 5]
b = [2, 3, 5, 7, 11]
print(difference(a, b))
The result will be [1, 4].
Tested on:
- Ubuntu 17.10, Python 3.6.3
- repl.it - Python3 Compiler
References:
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