Python Program to Filter Rows with a specific Pair Sum

Last Updated : 12 Nov, 2020

Given Matrix, the following program shows how to extract all rows which have a pair such that their sum is equal to a specific number, here denoted as K.

Input : test_list = [[1, 5, 3, 6], [4, 3, 2, 1], [7, 2, 4, 5], [6, 9, 3, 2]], k = 8
Output : [[1, 5, 3, 6], [6, 9, 3, 2]]
Explanation : 5 + 3 = 8 and 6 + 2 = 8.
Input : test_list = [[1, 5, 4, 6], [4, 3, 2, 1], [7, 2, 4, 5], [6, 9, 3, 7]], k = 8
Output : []
Explanation : No list with 8 as pair summation.

Method 1 : Using loop and list comprehension

In this we perform the task of getting all the pair whose sum is equal to a given value using external function and filtering of lists is done using list comprehension.

Python3

# get pair sum 
def pair_sum(x, k): 
  
    # checking pair sum 
    for idx in range(len(x)): 
        for ix in range(idx + 1, len(x)): 
            if x[idx] + x[ix] == k: 
                return True
    return False
  
  
# initializing list 
test_list = [[1, 5, 3, 6], [4, 3, 2, 1], [7, 2, 4, 5], [6, 9, 3, 2]] 
  
# printing original list 
print("The original list is : " + str(test_list)) 
  
# initializing K 
k = 8
  
# checking for pair sum 
res = [ele for ele in test_list if pair_sum(ele, k)] 
  
# printing result 
print("Filtered Rows : " + str(res)) 

Output:

The original list is : [[1, 5, 3, 6], [4, 3, 2, 1], [7, 2, 4, 5], [6, 9, 3, 2]]

Filtered Rows : [[1, 5, 3, 6], [6, 9, 3, 2]]

Method 2 : Using filter() and lambda

In this, we perform task of filtering using filter() and lambda function.

Python3

# get pair sum 
def pair_sum(x, k): 
  
    # checking pair sum 
    for idx in range(len(x)): 
        for ix in range(idx + 1, len(x)): 
            if x[idx] + x[ix] == k: 
                return True
    return False
  
  
# initializing list 
test_list = [[1, 5, 3, 6], [4, 3, 2, 1], [7, 2, 4, 5], [6, 9, 3, 2]] 
  
# printing original list 
print("The original list is : " + str(test_list)) 
  
# initializing K 
k = 8
  
# checking for pair sum 
# filtering using filter() and lambda 
res = list(filter(lambda ele: pair_sum(ele, k), test_list)) 
  
# printing result 
print("Filtered Rows : " + str(res)) 