Python Program to Extract Rows of a matrix with Even frequency Elements
Last Updated :
04 May, 2023
Given a Matrix, the task is to write a Python program to extract all the rows which have even frequencies of elements.
Examples:
Input: [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2], [6, 5, 6, 5], [1, 2, 3, 4]]
Output: [[4, 4, 4, 4, 2, 2], [6, 5, 6, 5]]
Explanation:
frequency of 4-> 4 which is even
frequency of 2-> 2 which is even
frequency of 6-> 2 which is even
frequency of 5-> 2 which is even
Method 1 : Using list comprehension, Counter() and all()
In this, count is maintained using Counter(), and all() is used to check if all frequencies are even, if not, row is not entered in result list.
Program:
Python3
from collections import Counter
test_list = [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2],
[6, 5, 6, 5], [1, 2, 3, 4]]
print("The original list is : " + str(test_list))
res = [sub for sub in test_list if all(
val % 2 == 0 for key, val in list(dict(Counter(sub)).items()))]
print("Filtered Matrix ? : " + str(res))
|
Output
The original list is : [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2], [6, 5, 6, 5], [1, 2, 3, 4]]
Filtered Matrix ? : [[4, 4, 4, 4, 2, 2], [6, 5, 6, 5]]
Time Complexity: O(M*N)
Auxiliary Space: O(K)
Method 2: Using filter(), Counter() and items()
Similar to the above method, the difference being filter() and lambda function is used for the task of filtering even frequency rows.
Program:
Python3
from collections import Counter
test_list = [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2],
[6, 5, 6, 5], [1, 2, 3, 4]]
print("The original list is : " + str(test_list))
res = list(filter(lambda sub: all(val % 2 == 0 for key,
val in list(dict(Counter(sub)).items())), test_list))
print("Filtered Matrix ? : " + str(res))
|
Output
The original list is : [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2], [6, 5, 6, 5], [1, 2, 3, 4]]
Filtered Matrix ? : [[4, 4, 4, 4, 2, 2], [6, 5, 6, 5]]
Time Complexity: O(m*n), where m and n is the number of rows and columns in the list “test_list”.
Auxiliary Space: O(k), where k is the number of elements
Method 3 : Using set() and count() methods
Python3
test_list = [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2],
[6, 5, 6, 5], [1, 2, 3, 4]]
print("The original list is : " + str(test_list))
res = []
for i in test_list:
x = set(i)
c = 0
for j in x:
if(i.count(j) % 2 == 0):
c += 1
if(c == len(x)):
res.append(i)
print("Filtered Matrix ? : " + str(res))
|
Output
The original list is : [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2], [6, 5, 6, 5], [1, 2, 3, 4]]
Filtered Matrix ? : [[4, 4, 4, 4, 2, 2], [6, 5, 6, 5]]
Method 4 : Using set() and operator.countOf() methods
Python3
import operator as op
test_list = [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2],
[6, 5, 6, 5], [1, 2, 3, 4]]
print("The original list is : " + str(test_list))
res = []
for i in test_list:
x = set(i)
c = 0
for j in x:
if(op.countOf(i,j) % 2 == 0):
c += 1
if(c == len(x)):
res.append(i)
print("Filtered Matrix ? : " + str(res))
|
Output
The original list is : [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2], [6, 5, 6, 5], [1, 2, 3, 4]]
Filtered Matrix ? : [[4, 4, 4, 4, 2, 2], [6, 5, 6, 5]]
Time Complexity: O(n*n )
Auxiliary Space: O(n*n)
Method 5: Using nested for loop +all()
Python3
test_list = [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2], [6, 5, 6, 5], [1, 2, 3, 4]]
print("The original list is : " + str(test_list))
result = []
for sub in test_list:
count = dict()
for ele in sub:
if ele % 2 == 0:
count[ele] = count.get(ele, 0) + 1
if all(val % 2 == 0 for val in count.values()):
result.append(sub)
print("Filtered Matrix ? : " + str(result))
|
Output
The original list is : [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2], [6, 5, 6, 5], [1, 2, 3, 4]]
Filtered Matrix ? : [[4, 4, 4, 4, 2, 2], [6, 5, 6, 5]]
Time Complexity: O(n*n)
Auxiliary Space: O(n)
Method 6: Using only built-in Python functions
Python3
test_list = [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2],
[6, 5, 6, 5], [1, 2, 3, 4]]
print("The original list is : " + str(test_list))
res = []
for row in test_list:
counts = {}
for elem in row:
counts[elem] = counts.get(elem, 0) + 1
if all(count % 2 == 0 for count in counts.values()):
res.append(row)
print("Filtered Matrix ? : " + str(res))
|
Output
The original list is : [[4, 5, 5, 2], [4, 4, 4, 4, 2, 2], [6, 5, 6, 5], [1, 2, 3, 4]]
Filtered Matrix ? : [[4, 4, 4, 4, 2, 2], [6, 5, 6, 5]]
Time complexity: O(n^2) where n is the size of the input list of lists.
Auxiliary space: O(n) to store the resulting list of lists.
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