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# Python – Inter Matrix Grouping

• Last Updated : 29 Aug, 2020

Given 2 Matrix, with 2 elements in each row, group them on basis on first element.

Input : test_list1 = [[2, 0], [8, 4], [9, 3]], test_list2 = [[8, 1], [9, 7], [2, 10]]
Output : {2: [0, 10], 8: [4, 1], 9: [3, 7]}
Explanation : All values after mapping cross Matrix, 2 mapped to 0 and 10.

Input : test_list1 = [[8, 4], [9, 3]], test_list2 = [[8, 1], [9, 7]]
Output : {8: [4, 1], 9: [3, 7]}
Explanation : All values after mapping cross Matrix.

Method #1 : Using defaultdict() + loop

This is one of the ways in which this task can be performed. In this, we iterate add both the lists and then form groups from similar elements and convert to dictionary with value list.

## Python3

 `# Python3 code to demonstrate working of ``# Inter Matrix Grouping``# Using defaultdict() + loop``from` `collections ``import` `defaultdict`` ` `# initializing lists``test_list1 ``=` `[[``5``, ``8``], [``2``, ``0``], [``8``, ``4``], [``9``, ``3``]]``test_list2 ``=` `[[``8``, ``1``], [``9``, ``7``], [``2``, ``10``], [``5``, ``6``]]`` ` `# printing original list``print``(``"The original list 1 : "` `+` `str``(test_list1))``print``(``"The original list 2 : "` `+` `str``(test_list2))`` ` `# initializing mapping list ``res ``=` `defaultdict(``list``)`` ` `# concatenation matrix using 2 lists``for` `key, val ``in` `test_list1 ``+` `test_list2:``    ``res[key].append(val)`` ` `# printing result ``print``(``"The Grouped Matrix : "` `+` `str``(``dict``(res)))`
Output
```The original list 1 : [[5, 8], [2, 0], [8, 4], [9, 3]]
The original list 2 : [[8, 1], [9, 7], [2, 10], [5, 6]]
The Grouped Matrix : {5: [8, 6], 2: [0, 10], 8: [4, 1], 9: [3, 7]}
```

Method #2 : Using dictionary comprehension + dict()

This is yet another way in which this task can be performed. In this, we iterate for all the elements of both matrix by converting each to dictionary and group its values. Its important to have traces of each element’s mapping in both the Matrix.

## Python3

 `# Python3 code to demonstrate working of ``# Inter Matrix Grouping``# Using dictionary comprehension + dict()`` ` `# initializing lists``test_list1 ``=` `[[``5``, ``8``], [``2``, ``0``], [``8``, ``4``], [``9``, ``3``]]``test_list2 ``=` `[[``8``, ``1``], [``9``, ``7``], [``2``, ``10``], [``5``, ``6``]]`` ` `# printing original list``print``(``"The original list 1 : "` `+` `str``(test_list1))``print``(``"The original list 2 : "` `+` `str``(test_list2))`` ` `# mapping dictionaries together, converting each row to dictionary``res ``=` `{key: [``dict``(test_list1)[key], ``dict``(test_list2)[key]] ``for` `key ``in` `dict``(test_list1)}`` ` `# printing result ``print``(``"The Grouped Matrix : "` `+` `str``(``dict``(res)))`
Output
```The original list 1 : [[5, 8], [2, 0], [8, 4], [9, 3]]
The original list 2 : [[8, 1], [9, 7], [2, 10], [5, 6]]
The Grouped Matrix : {5: [8, 6], 2: [0, 10], 8: [4, 1], 9: [3, 7]}
```

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