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# Python | Custom length Matrix

• Last Updated : 02 Jan, 2023

Sometimes, we need to initialize a matrix in Python of variable length from the list containing elements. In this article, we will discuss the variable length method initialization and certain shorthands to do so. Let’s discuss certain ways to perform this. Method #1 : Using zip() + list comprehension The zip function combined with the list comprehension can help to achieve this particular task. The zip function can help to zip the counter list with the element list and list comprehension does the work of construction of matrix.

## Python3

 `# Python3 code to demonstrate ``# Custom length Matrix``# using zip() + list comprehension` `# initializing list``test_list ``=` `[``'a'``, ``'b'``, ``'c'``]` `# initializing counter list``counter_list ``=` `[``1``, ``4``, ``2``]` `# printing original list``print` `("The original ``list` `is` `: " ``+` `str``(test_list))` `# printing counter list``print` `("The counter ``list` `is` `: " ``+` `str``(counter_list))` `# using zip() + list comprehension``# Custom length Matrix``res ``=` `[[i] ``*` `j ``for` `i, j ``in` `zip``(test_list, counter_list)]` `# printing result``print` `("The custom length matrix ``is` `: " ``+` `str``(res))`

Output :

```The original list is : ['a', 'b', 'c']
The counter list is : [1, 4, 2]
The custom length matrix is : [['a'], ['b', 'b', 'b', 'b'], ['c', 'c']]```

Method #2 : Using map() + mul operator This particular problem can also be solved using the inbuilt mul operator which performs multiplication of liked index elements and map function performs the task of formation of matrix.

## Python3

 `# Python3 code to demonstrate ``# Custom length Matrix``# using map() + mul operator``from` `operator ``import` `mul` `# initializing list``test_list ``=` `[``'a'``, ``'b'``, ``'c'``]` `# initializing counter list``counter_list ``=` `[``1``, ``4``, ``2``]` `# printing original list``print` `("The original ``list` `is` `: " ``+` `str``(test_list))` `# printing counter list``print` `("The counter ``list` `is` `: " ``+` `str``(counter_list))` `# using map() + mul operator``# Custom length Matrix``res ``=` `list``(``map``(mul, [[``'a'``], [``'b'``], [``'c'``]], counter_list))` `# printing result``print` `("The custom length matrix ``is` `: " ``+` `str``(res))`

Output :

```The original list is : ['a', 'b', 'c']
The counter list is : [1, 4, 2]
The custom length matrix is : [['a'], ['b', 'b', 'b', 'b'], ['c', 'c']]```

Method #3 : Using looping + *:  Here is another approach using a for loop and the * operator:

## Python3

 `# Initialize the lists``test_list ``=` `[``'a'``, ``'b'``, ``'c'``]``counter_list ``=` `[``1``, ``4``, ``2``]` `# Initialize the result list``result ``=` `[]` `# Iterate through the lists``for` `i, j ``in` `zip``(test_list, counter_list):``    ``# Append the element from test_list repeated j times to the result list``    ``result.append([i] ``*` `j)` `# Print the original lists``print``(``"The original list is :"``, test_list)``print``(``"The counter list is :"``, counter_list)` `# Print the result``print``(``"The custom length matrix is :"``, result)``#This code is contributed by Edula Vinay Kumar Reddy`

Output

```The original list is : ['a', 'b', 'c']
The counter list is : [1, 4, 2]
The custom length matrix is : [['a'], ['b', 'b', 'b', 'b'], ['c', 'c']]```

This approach iterates through the test_list and counter_list using the zip() function, and for each element and its corresponding count, it appends a list containing the element repeated j times to the result list using the * operator.

For example, given the lists [‘a’, ‘b’, ‘c’] and [1, 4, 2], the resulting list would be [[‘a’], [‘b’, ‘b’, ‘b’, ‘b’], [‘c’, ‘c’]].

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