# Python Program to Extract Rows of a matrix with Even frequency Elements

• Last Updated : 24 Jan, 2021

Given a Matrix, the task is to write a Python program to extract all the rows which have even frequencies of elements.

Examples:

Input: [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2], [6, 5, 6, 5], [1, 2, 3, 4]]

Output: [[4, 4, 4, 4, 2, 2], [6, 5, 6, 5]]

Explanation:

• frequency of 4-> 4 which is even
• frequency of 2-> 2 which is even
• frequency of 6-> 2 which is even
• frequency of 5-> 2 which is even

Method 1 : Using list comprehension, Counter() and all()

In this, count is maintained using Counter(), and all() is used to check if all frequencies are even, if not, row is not entered in result list.

Program:

## Python3

 `from` `collections ``import` `Counter`` ` `# initializing list``test_list ``=` `[[``4``, ``5``, ``5``, ``2``], [``4``, ``4``, ``4``, ``4``, ``2``, ``2``],``             ``[``6``, ``5``, ``6``, ``5``], [``1``, ``2``, ``3``, ``4``]]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# Counter() gets the required frequency``res ``=` `[sub ``for` `sub ``in` `test_list ``if` `all``(``    ``val ``%` `2` `=``=` `0` `for` `key, val ``in` `list``(``dict``(Counter(sub)).items()))]`` ` `# printing result``print``(``"Filtered Matrix ? : "` `+` `str``(res))`

Output:

The original list is : [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2], [6, 5, 6, 5], [1, 2, 3, 4]]

Filtered Matrix ? : [[4, 4, 4, 4, 2, 2], [6, 5, 6, 5]]

Method 2 : Using filter(), Counter() and items()

Similar to above method, difference being filter() and lambda function is used for the task of filtering even frequency rows.

Program:

## Python3

 `from` `collections ``import` `Counter`` ` `# initializing list``test_list ``=` `[[``4``, ``5``, ``5``, ``2``], [``4``, ``4``, ``4``, ``4``, ``2``, ``2``], ``             ``[``6``, ``5``, ``6``, ``5``], [``1``, ``2``, ``3``, ``4``]]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# Counter() gets the required frequency``# filter() used to perform filtering``res ``=` `list``(``filter``(``lambda` `sub: ``all``(val ``%` `2` `=``=` `0` `for` `key,``                                  ``val ``in` `list``(``dict``(Counter(sub)).items())), test_list))`` ` `# printing result``print``(``"Filtered Matrix ? : "` `+` `str``(res))`

Output:

The original list is : [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2], [6, 5, 6, 5], [1, 2, 3, 4]]

Filtered Matrix ? : [[4, 4, 4, 4, 2, 2], [6, 5, 6, 5]]

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