Question

How can I form an array (c) composed of elements of b which are not in a?

a=[1,2,"ID123","ID126","ID124","ID125"]
b=[1,"ID123","ID124","ID125","343434","fffgfgf"]
c= []

Can this be done without using a list comprehension?

Answer 1

If the lists are long, you want to make a set of a first:

a_set = set(a)
c = [x for x in b if x not in a_set]

If the order of the elements don’t matter, then just use sets:

c = list(set(b) - set(a))

Python lists don’t offer a direct - operator, as Ruby arrays do.