# Python – Count similar pair in Dual List

Sometimes, while working with data, we can have a problem in which we receive the dual elements pair and we intend to find pairs of similar elements and it’s frequency. This kind of data is usually useful in data domains. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using `Counter() + map() + sorted() + items()`
The combination of above functions can be used to achieve this particular task. In this, we first find frequency using Counter and then link it in a tuple using map(). The sorted() peforms task of sorting before using above method.

 `# Python3 code to demonstrate  ` `# Count Similar pair in dual list ` `# using Counter() + map() + sorted() + items() ` `from` `collections ``import` `Counter ` ` `  `# initializing list  ` `test_list ``=` `[[``1``, ``2``], [``2``, ``1``], [``3``, ``4``], [``4``, ``3``], [``5``, ``4``]] ` ` `  `# printing original list ` `print` `(``"The original list is : "` `+` `str``(test_list)) ` ` `  `# Count Similar pair in dual list ` `# using Counter() + map() + sorted() + items() ` `temp ``=` `[``sorted``(ele) ``for` `ele ``in` `test_list] ` `res ``=` `[(i, j, k) ``for` `(i, j), k ``in` `Counter(``map``(``tuple``, temp)).items()] ` ` `  `# printing result  ` `print` `(``"The dual list similarity counts : "` `+` `str``(res)) `

Output :

```The original list is : [[1, 2], [2, 1], [3, 4], [4, 3], [5, 4]]
The dual list similarity counts : [(1, 2, 2), (4, 5, 1), (3, 4, 2)]
```

Method #2 : Using `sum() + list comprehension + groupby() + sorted()`
In this method, the task of counting is performed using sum() and task of getting group is performed using groupby().

 `# Python3 code to demonstrate  ` `# Count Similar pair in dual list ` `# using sum() + list comprehension + groupby() + sorted() ` `from` `itertools ``import` `groupby ` ` `  `# initializing list  ` `test_list ``=` `[[``1``, ``2``], [``2``, ``1``], [``3``, ``4``], [``4``, ``3``], [``5``, ``4``]] ` ` `  `# printing original list ` `print` `(``"The original list is : "` `+` `str``(test_list)) ` ` `  `# Count Similar pair in dual list ` `# using sum() + list comprehension + groupby() + sorted() ` `res ``=` `[(``*``temp, ``sum``(``1` `for` `idx ``in` `elements)) ` `      ``for` `temp, elements ``in` `groupby(test_list, key ``=` `lambda` `j : ``sorted``(j))] ` ` `  `# printing result  ` `print` `(``"The dual list similarity counts : "` `+` `str``(res)) `

Output :

```The original list is : [[1, 2], [2, 1], [3, 4], [4, 3], [5, 4]]
The dual list similarity counts : [(1, 2, 2), (4, 5, 1), (3, 4, 2)]
```

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