# Python | Combine two lists by maintaining duplicates in first list

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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