Python | Find common elements in list of lists

• Last Updated : 12 Feb, 2019

The problem of finding the common elements in list of 2 lists is quite a common problem and can be dealt with ease and also has been discussed before many times. But sometimes, we require to find the elements that are in common from N lists. Let’s discuss certain ways in which this operation can be performed.

Method #1 : Using `reduce() + lambda + set()`
This particular task can be achieved in just a one line using the combination of the above functions. The reduce function can be used to operate the function of “&” operation to all the list. The set function can be used to convert list into a set to remove repetition.

 `# Python3 code to demonstrate ``# common element extraction form N lists ``# using reduce() + lambda + set()``from` `functools ``import` `reduce`` ` `# initializing list of lists``test_list ``=` `[[``2``, ``3``, ``5``, ``8``], [``2``, ``6``, ``7``, ``3``], [``10``, ``9``, ``2``, ``3``]]`` ` `# printing original list``print` `(``"The original list is : "` `+` `str``(test_list))`` ` `# common element extraction form N lists``# using reduce() + lambda + set()``res ``=` `list``(``reduce``(``lambda` `i, j: i & j, (``set``(x) ``for` `x ``in` `test_list)))`` ` `# printing result``print` `(``"The common elements from N lists : "` `+` `str``(res))`

Output:

```The original list is : [[2, 3, 5, 8], [2, 6, 7, 3], [10, 9, 2, 3]]
The common elements from N lists : [2, 3]
```

Method #2 : Using `map() + intersection()`
The `map `function can be used to convert each of the lists to set to be operated by to perform the intersection, using the set.intersection function. This is the most elegant way to perform this particular task.

 `# Python3 code to demonstrate ``# common element extraction form N lists ``# using map() + intersection()`` ` `# initializing list of lists``test_list ``=` `[[``2``, ``3``, ``5``, ``8``], [``2``, ``6``, ``7``, ``3``], [``10``, ``9``, ``2``, ``3``]]`` ` `# printing original list``print` `(``"The original list is : "` `+` `str``(test_list))`` ` `# common element extraction form N lists``# using map() + intersection()``res ``=` `list``(``set``.intersection(``*``map``(``set``, test_list)))`` ` `# printing result``print` `(``"The common elements from N lists : "` `+` `str``(res))`

Output:

```The original list is : [[2, 3, 5, 8], [2, 6, 7, 3], [10, 9, 2, 3]]
The common elements from N lists : [2, 3]
```

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