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Python | Common Row elements Summation
• Last Updated : 19 Feb, 2020

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 and return their sum. Let’s discuss certain ways in which this operation can be performed.

Method #1 : Using `reduce() + lambda + set() + sum()`
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. The task of performing sum is done using sum().

 `# Python code to demonstrate ``# Common Row elements Summation``# using reduce() + lambda + set() + sum()`` ` `# 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 Row elements Summation``# using reduce() + lambda + set() + sum()``res ``=` `sum``(``list``(``reduce``(``lambda` `i, j: i & j, (``set``(x) ``for` `x ``in` `test_list))))`` ` `# printing result``print` `(``"The common row elements sum is : "` `+` `str``(res))`
Output :
```The original list is : [[2, 3, 5, 8], [2, 6, 7, 3], [10, 9, 2, 3]]
The common row elements sum is : 5
```

Method #2 : Using `map() + intersection() + sum()`
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. The task of performing sum is done using sum().

 `# Python3 code to demonstrate ``# Common Row elements Summation``# using map() + intersection() + sum()`` ` `# 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 Row elements Summation``# using map() + intersection() + sum()``res ``=` `sum``(``list``(``set``.intersection(``*``map``(``set``, test_list))))`` ` `# printing result``print` `(``"The common row elements sum is : "` `+` `str``(res))`
Output :
```The original list is : [[2, 3, 5, 8], [2, 6, 7, 3], [10, 9, 2, 3]]
The common row elements sum is : 5
```

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