Python Program to Filter Rows with a specific Pair Sum

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))

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]]