Python | Row lengths in Matrix

The problems concerning matrix are quite common in both competitive programming and Data Science domain. One such problem that we might face is of finding the lengths of rows of matrix in uneven sized matrix. Let’s discuss certain ways in which this problem can be solved.

Method #1 : Using max() + map() + sum() + list comprehension

The combination of above functions can help to get the solution to this particular problem in just a one line and hence quite useful. The sum function computes the sum of sublists, max function can be used to order in descending and all this bound together using list comprehension.



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# Python3 code to demonstrate
# Row lengths in matrix
# using max() + map() + sum() + list comprehension
  
# initializing list
test_list = [[4, 5, 6], [7, 8], [2]]
  
# printing original list
print("The original list : " + str(test_list))
  
# using max() + map() + sum() + list comprehension
# Row lengths in matrix
res = [sum(len(row) > idx for row in test_list)
    for idx in range(max(map(len, test_list)))]
  
# print result
print("The row lengths in matrix : " + str(res))

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Output :

The original list : [[4, 5, 6], [7, 8], [2]]
The row lengths in matrix : [3, 2, 1]

 

Method #2 : Using sum() + filter() + zip_longest()

This problem can also be solved using the set of functions above. The filter function can be used to get the separate lists and the task of binding for summation done by sum function is performed by zip_longest function.

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# Python3 code to demonstrate
# Row lengths in matrix
# using sum() + filter() + zip_longest()
from itertools import zip_longest
  
# initializing list
test_list = [[4, 5, 6], [7, 8], [2]]
  
# printing original list
print("The original list : " + str(test_list))
  
# using sum() + filter() + zip_longest()
# Row lengths in matrix
res = [sum(1 for idx in filter(None.__ne__, i))
              for i in zip_longest(*test_list)]
  
# print result
print("The row lengths in matrix : " + str(res))

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Output :

The original list : [[4, 5, 6], [7, 8], [2]]
The row lengths in matrix : [3, 2, 1]


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