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# Python – Test Common Elements Order

• Last Updated : 01 Mar, 2020

Sometimes, while working with lists, we can have a problem in which we need to test if list containes common elements. This type of problem has been dealt many times and has lot of solutions. But sometimes, we might have a problem in which we need to check that those common elements appear in same order in both list or not. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using loop + `set()`
The combination of above functions can be used to perform this task. In this, we iterate through the lists and check using conditions of we have in order common elements or not. The duplication removal is performed using set().

 `# Python3 code to demonstrate ``# Test Common Elements Order``# using loop + set()`` ` `# helper function``def` `common_ord(test_list1, test_list2):``    ``comm ``=` `set``(test_list1)``    ``comm.intersection_update(test_list2)``    ``pr_idx ``=` `0``    ``for` `ele ``in` `test_list1:``        ``if` `ele ``in` `comm:``            ``try``:``                ``pr_idx ``=` `test_list2.index(ele, pr_idx)``            ``except` `ValueError:``                ``return` `False``    ``return` `True`` ` `# Initializing lists``test_list1 ``=` `[``'Gfg'``, ``'is'``, ``'for'``, ``'Geeks'``]``test_list2 ``=` `[``1``, ``'Gfg'``, ``2``, ``'Geeks'``]`` ` `# printing original lists``print``(``"The original list 1 is : "` `+` `str``(test_list1))``print``(``"The original list 2 is : "` `+` `str``(test_list2))`` ` `# Test Common Elements Order``# using loop + set()``res ``=` `common_ord(test_list1, test_list2)`` ` `# printing result ``print` `(``"Are common elements in order ? : "` `+` `str``(res))`
Output :
```The original list 1 is : ['Gfg', 'is', 'for', 'Geeks']
The original list 2 is : [1, 'Gfg', 2, 'Geeks']
Are common elements in order ? : True
```

Method #2 : Using list comprehension + `set()`
The combination of above functions perform the task in similar way. The difference is that we use shorter constructs as compared to upper method.

 `# Python3 code to demonstrate ``# Test Common Elements Order``# using list comprehension + set()`` ` `# Initializing lists``test_list1 ``=` `[``'Gfg'``, ``'is'``, ``'for'``, ``'Geeks'``]``test_list2 ``=` `[``1``, ``'Gfg'``, ``2``, ``'Geeks'``]`` ` `# printing original lists``print``(``"The original list 1 is : "` `+` `str``(test_list1))``print``(``"The original list 2 is : "` `+` `str``(test_list2))`` ` `# Test Common Elements Order``# using list comprehension + set()``temp ``=` `set``(test_list1) & ``set``(test_list2)``temp1 ``=` `[val ``for` `val ``in` `test_list1 ``if` `val ``in` `temp]``temp2 ``=` `[val ``for` `val ``in` `test_list2 ``if` `val ``in` `temp]``res ``=` `temp1 ``=``=` `temp2`` ` `# printing result ``print` `(``"Are common elements in order ? : "` `+` `str``(res))`
Output :
```The original list 1 is : ['Gfg', 'is', 'for', 'Geeks']
The original list 2 is : [1, 'Gfg', 2, 'Geeks']
Are common elements in order ? : True
```

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