# Get Union of Lists in Python

- Get Union of Two lists with repetition of common elements in Python
- Get Union of two List in sorted order in Python
- Get Union of Two Lists without repetition of common elements in Python
- Get Union of More than Two Lists in Python

Union of lists means that all the elements from the different lists will be put up inside a single list. We can find a union of two or more than two lists. There are various methods to achieve a Union of Lists. All the methods are described below with sufficient code examples.

## Get Union of Two lists with repetition of common elements in Python

We can add two lists using the `+`

operator to get the union of the two lists.

Example code:

```
l1 = [1,2,3,4,5]
l2 = [2,4,6.8,10]
l3 = l1 + l2
print("l1: ",l1)
print("l2: ",l2)
print("Union of l1 and l2 with element repetition: ",l3)
```

Output:

```
l1: [1, 2, 3, 4, 5]
l2: [2, 4, 6.8, 10]
Union of l1 and l2 with element repetition: [1, 2, 3, 4, 5, 2, 4, 6.8, 10]
```

It finds the union of the lists `l1`

and `l2`

and stores the result in `l3`

. From the output, it is clear that we have repeated elements while finding union if we have the same element repeated in any of the list operands.

## Get Union of two List in sorted order in Python

If we wish to find the union of Lists in a sorted manner, we use the `sorted()`

method to sort the list obtained after union operation.

Code :

```
l1 = [11,20,1,2,3,4,5]
l2 = [2,4,6,8,10]
union_l1_l2 = l1+l2
l3 = sorted(union_l1_l2)
print("l1: ",l1)
print("l2: ",l2)
print("Sorted union of two l1 and l2 : ",l3)
```

Output:

```
l1: [11, 20, 1, 2, 3, 4, 5]
l2: [2, 4, 6, 8, 10]
Sorted union of two l1 and l2 : [1, 2, 2, 3, 4, 4, 5, 6, 8, 10, 11, 20]
```

It computes the union of lists `l1`

and `l2`

using the `+`

operator and stores the union in `union_l1_l2`

. We use the `sorted()`

method to sort the elements of the list `union_l1_l2`

to get the union of `l1`

and `l2`

in a sorted fashion.

## Get Union of Two Lists without repetition of common elements in Python

In Python, sets are the data types that do not allow duplication of elements. So, we can use `set()`

to get the union of two lists without repetition of common elements.

Code :

```
def union_without_repetition(list1,list2):
result = list(set(list1 + list2))
return result
l1 = [1,2,3,4,5]
l2 = [2,4,6,8,10]
l3= union_without_repetition(l1,l2)
print("l1: ",l1)
print("l2: ",l2)
print("Union of two l1 and l2 without repetition : ",l3)
```

Output:

```
l1: [1, 2, 3, 4, 5]
l2: [2, 4, 6, 8, 10]
Union of two l1 and l2 without repetition : [1, 2, 3, 4, 5, 6, 8, 10]
```

Here, we find the union of `l1`

and `l2`

using the `+`

operator and select only unique elements using the `set()`

function and then finally convert the set into a list using the `list()`

function.

## Get Union of More than Two Lists in Python

We have already computed the union of the two lists. But, what to do in the case of finding a union of more than two lists. It is very simple. We can use both the `set()`

and `union()`

inbuilt python function to find the union of more than two lists.

Code :

```
def union(lst1, lst2, lst3):
final_list = list(set().union(lst1, lst2, lst3))
return final_list
l1 = [1,2,3,4,5]
l2 = [2,4,6,8,10]
l3 = [5,6,7,8,11,15,18]
print("l1: ",l1)
print("l2: ",l2)
print("l3 : ",l3)
print("Union of more than l1 l2 and l3: ",union(l1,l2,l3))
```

Output:

```
l1: [1, 2, 3, 4, 5]
l2: [2, 4, 6, 8, 10]
l3 : [5, 6, 7, 8, 11, 15, 18]
Union of more than l1 l2 and l3: [1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 15, 18]
```

Here, we create a `set`

object using `set()`

constructor and then call `union()`

method for the object. The `union()`

method can take any number of `list`

objects and return their union.

In this case, as we are using the `union()`

method of the `set`

class, we don’t get repeated elements.