Python: Combining Two Lists And Removing Duplicates In A Functional Programming Way

I'm trying to write a function that would combine two lists while removing duplicate items, but in a pure functional way. For example: a = [1,2,2] b = [1,3,3,4,5,0] union(a,b) --&g

Solution 1:

list(set(a + b))

This combines two lists a and b and using set takes only unique vales and then we can make it back to list.

Solution 2:

If you want to keep the order you can use collections.OrderedDict, otherwise just use set. These data structures use hash values of their items for preserving them, thus they don't keep the duplicates.

In [11]: from collections import OrderedDict

In [12]: list(OrderedDict.fromkeys(a+b))
Out[12]: [1, 2, 3, 4, 5, 0]

Solution 3:

Have you tried using sets?

>>> a = [1,2,2]
>>> b = [1,3,3,4,5,0]
>>> list(set(a).union(set(b)))
[0, 1, 2, 3, 4, 5]

Solution 4:

To combine the two lists:

a = [1,2,2]
b = [1,3,3,4,5,0]

Using sets:

union = set(a) | set(b)
# -> set([0, 1, 2, 3, 4, 5])

Using comprehension list:

union = a + [x for x in b if x not in a]
# -> [1, 2, 2, 3, 3, 4, 5, 0]

Using loop, without duplicates, preserving order:

union = []
for x in a + b:
    if x not in union:
        union.append(x)
# -> [1, 2, 3, 4, 5, 0]

Solution 5:

How about

>>> x = [1,2,3]
>>> y = [1,3,5,7,9]
>>> list(set(x).union(set(y)))