Custom length Matrix in Python

Sometimes when creating a matrix using Python, we may need to control how many times a given element is repeated in the resulting matrix. In this article, we will see how to create a matrix with a required number of elements when the elements are given as a list.

Using zip() and List Comprehension

We declare a list with elements to be used in the matrix. Then we declare another list which will hold the number of occurrences of the element in the matrix. Using the zip() function with list comprehension, we can create the resulting matrix ?

Example

elements = ['m', 'n', 'p', 'q']

# Count of elements
elem_count = [1, 0, 3, 2]

# Given Lists
print("Given List of elements:", elements)
print("Count of elements:", elem_count)

# Creating Matrix
matrix = [[x] * y for x, y in zip(elements, elem_count)]

# Result
print("The new matrix is:", matrix)

Given List of elements: ['m', 'n', 'p', 'q']
Count of elements: [1, 0, 3, 2]
The new matrix is: [['m'], [], ['p', 'p', 'p'], ['q', 'q']]

Using map() with operator.mul

In this approach, we use the mul method from the operator module. The map() function applies the multiplication operation to every element pair, creating repeated strings instead of lists ?

Example

from operator import mul

elements = ['m', 'n', 'p', 'q']

# Count of elements
elem_count = [1, 0, 3, 2]

# Given Lists
print("Given List of elements:", elements)
print("Count of elements:", elem_count)

# Creating Matrix (as repeated strings)
matrix = list(map(mul, elements, elem_count))

# Result
print("The new matrix is:", matrix)

Given List of elements: ['m', 'n', 'p', 'q']
Count of elements: [1, 0, 3, 2]
The new matrix is: ['m', '', 'ppp', 'qq']

Comparison

Conclusion

Use zip() with list comprehension when you need a proper matrix structure with sublists. Use map() with operator.mul for simple string repetition operations.