Python | Combine two lists by maintaining duplicates in first list

• Last Updated : 07 Mar, 2019

Given two lists, the task is to combine two lists and removing duplicates, without removing duplicates in original list.

Example:

```Input :
list_1 = [11, 22, 22, 15]
list_2 = [22, 15, 77, 9]

Output :
OutList = [11, 22, 22, 15, 77, 9]```

Code #1: using extend

 `# Python code to combine two lists``# and removing duplicates, without``# removing duplicates in original list.`` ` `# Initialisation of first list``list1 ``=` `[``111``, ``222``, ``222``, ``115``]`` ` `# Initialisation of Second list``list2 ``=` `[``222``, ``115``, ``77``, ``19``]`` ` `output ``=` `list``(list1)`` ` `# Using extend function``output.extend(y ``for` `y ``in` `list2 ``if` `y ``not` `in` `output)`` ` `# printing result``print``(output)`
Output:
```[111, 222, 222, 115, 77, 19]
```

Code #2 : Using Set and Iteration
Append those element in first list which are not in second list and then take union of first and second list.

 `# Python code to combine two lists ``# and removing duplicates, without ``# removing duplicates in original list.`` ` `# Initialisation of first list``list1 ``=` `[``11``, ``22``, ``22``, ``15``]`` ` `# Initialisation of Second list``list2 ``=` `[``22``, ``15``, ``77``, ``9``]`` ` `# creating set``unique_list1 ``=` `set``(list1)``unique_list2 ``=` `set``(list2)`` ` `# Difference in two sets``diff_element ``=` `unique_list2 ``-` `unique_list1`` ` `# union of difference + first list``output ``=` `list1 ``+` `list``(diff_element)`` ` `# printing output``print``(output) `
Output:
```[11, 22, 22, 15, 9, 77]
```

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