Related Articles

# Python – Custom Columns Matrix

• Last Updated : 03 Jul, 2020

Sometimes, while working with Python lists, we can have a problem in which we need to extract certain columns from Matrix and recreate it. This kind of problem can have applications in data domains as they use Matrix as a prominent input parameter. Let’s discuss certain ways in which this task can be performed.

Input : test_list = [[5, 4, 3, 4], [7, 6, 3, 2], [8, 3, 9, 10]], col_list = 
Output : [, , ]

Attention geek! Strengthen your foundations with the Python Programming Foundation Course and learn the basics.

To begin with, your interview preparations Enhance your Data Structures concepts with the Python DS Course. And to begin with your Machine Learning Journey, join the Machine Learning - Basic Level Course

Input : test_list = [[5, 4], [6, 2], [8, 3]], col_list = 
Output : [, , ]

Method #1 : Using list comprehension
This offers one of the ways to solve this problem. In this, we perform extraction of selective columns using nested list comprehension.

 `# Python3 code to demonstrate working of ``# Custom Columns Matrix``# Using list comprehension`` ` `# initializing list``test_list ``=` `[[``5``, ``4``, ``3``, ``4``],``             ``[``7``, ``6``, ``3``, ``2``], ``             ``[``8``, ``3``, ``9``, ``10``]]`` ` `# printing original list ``print``(``"The original list : "` `+` `str``(test_list))`` ` `# initializing Columns list ``col_list ``=` `[``1``, ``3``]`` ` `# Custom Columns Matrix``# Using list comprehension``res ``=` `[[sub[idx] ``for` `idx ``in` `col_list] ``for` `sub ``in` `test_list]`` ` `# printing result ``print``(``"Matrix after filtering : "` `+` `str``(res))`
Output :
```The original list : [[5, 4, 3, 4], [7, 6, 3, 2], [8, 3, 9, 10]]
Matrix after filtering : [[4, 4], [6, 2], [3, 10]]
```

Method #2 : Using `itemgetter()` + list comprehension
The combination of above functions can be used to solve this problem. In this, we perform the task of getting indices using itemgetter().

 `# Python3 code to demonstrate working of ``# Custom Columns Matrix``# Using itemgetter() + list comprehension``from` `operator ``import` `itemgetter`` ` `# initializing list``test_list ``=` `[[``5``, ``4``, ``3``, ``4``],``             ``[``7``, ``6``, ``3``, ``2``], ``             ``[``8``, ``3``, ``9``, ``10``]]`` ` `# printing original list ``print``(``"The original list : "` `+` `str``(test_list))`` ` `# initializing Columns list ``col_list ``=` `[``1``, ``3``]`` ` `# Custom Columns Matrix``# Using itemgetter() + list comprehension``res ``=` `[``list``(itemgetter(``*``col_list)(ele)) ``for` `ele ``in` `test_list]`` ` `# printing result ``print``(``"Matrix after filtering : "` `+` `str``(res))`
Output :
```The original list : [[5, 4, 3, 4], [7, 6, 3, 2], [8, 3, 9, 10]]
Matrix after filtering : [[4, 4], [6, 2], [3, 10]]
```

My Personal Notes arrow_drop_up