Python – Consecutive Kth column Difference in Tuple List

Sometimes, while working with Python list, we can have a task in which we need to work with tuple list and get the absolute difference of it’s Kth index. This problem has application in web development domain while working with data informations. Let’s discuss certain ways in which this task can be performed.

Examples:

Input : test_list = [(5, 4, 2), (1, 3, 4), (5, 7, 8), (7, 4, 3)], K = 0 
Output : [4, 4, 2] 
Explanation : 5 – 1 = 4, hence 4. 

Input : test_list = [(5, 4, 2), (1, 3, 4), (5, 7, 8), (7, 4, 3)], K = 2 
Output : [2, 4, 5] 
Explanation : 8 – 3 = 5, hence 5. 

Method #1: Using loop

In this, for each tuple we subtract and find absolute difference of Kth column tuples with consecutive tuples in list.

Step-by-step approach :

• Initializes a variable K to 1, which represents the index of the column we want to compare.
• Creates an empty list res to store the absolute differences.
• Loops through the range of indices from 0 to the second-to-last index of the list using a for loop and the range() function. This is done to avoid going out of bounds of the list.
• Inside the loop, the program calculates the absolute difference between the Kth column of the current tuple and the Kth column of the next tuple using the abs() function, and appends the result to the res list.
• After the loop finishes, the program prints the resultant tuple list using the print() function and str() function to convert the list to a string.
• The program execution ends.

Below is the implementation of the above approach:

Python3

# Python3 code to demonstrate working of
# Consecutive Kth column Difference in Tuple List
# Using loop

# initializing list
test_list = [(5, 4, 2), (1, 3, 4), (5, 7, 8), (7, 4, 3)]

# printing original list
print("The original list is : " + str(test_list))

# initializing K
K = 1

res = []
for idx in range(0, len(test_list) - 1):

    # getting difference using abs()
    res.append(abs(test_list[idx][K] - test_list[idx + 1][K]))

# printing result
print("Resultant tuple list : " + str(res))

Output:

The original list is : [(5, 4, 2), (1, 3, 4), (5, 7, 8), (7, 4, 3)] Resultant tuple list : [1, 4, 3]

Time complexity: O(n), where n is the length of the input list test_list.
Auxiliary space: O(n),

Method #2: Using zip() + list comprehension

In this, we iterate for all the element in list using list comprehension and compare elements paired using zip(). 

Python3

# Python3 code to demonstrate working of
# Consecutive Kth column Difference in Tuple List
# Using zip() + list comprehension

# initializing list
test_list = [(5, 4, 2), (1, 3, 4), (5, 7, 8), (7, 4, 3)]

# printing original list
print("The original list is : " + str(test_list))

# initializing K
K = 1

# zip used to pair each tuple with subsequent tuple
res = [abs(x[K] - y[K]) for x, y in zip(test_list, test_list[1:])]

# printing result
print("Resultant tuple list : " + str(res))

Output:

The original list is : [(5, 4, 2), (1, 3, 4), (5, 7, 8), (7, 4, 3)] Resultant tuple list : [1, 4, 3]

Time complexity: O(n), where n is the length of the input list.
Auxiliary space: O(n), as it creates a new list of size n to store the result.

Method #3: Using numpy library .

• Initializes a list of tuples called test_list with four tuples containing three integers each.
• The original list is printed using the print() function and string concatenation.
• Initializes a variable called K with the value 1.
• Converts the list of tuples to a NumPy array using the np.array() function and assigns it to a variable called arr.
• Use NumPy to calculate the absolute difference between consecutive elements of the Kth column of the array using the np.abs() and np.diff() functions, and assigns the result to a variable called res.
• Prints the resulting list of differences using the list() function to convert the NumPy array to a Python list and the print() function with string concatenation.

Python3

import numpy as np

# initializing list
test_list = [(5, 4, 2), (1, 3, 4), (5, 7, 8), (7, 4, 3)]

# printing original list
print("The original list is : " + str(test_list))

# initializing K
K = 1

# convert the tuple list to a numpy array
arr = np.array(test_list)

# calculate the consecutive Kth column difference using numpy
res = np.abs(np.diff(arr[:, K]))

# printing result
print("Resultant tuple list : " + str(list(res)))

OUTPUT:
The original list is : [(5, 4, 2), (1, 3, 4), (5, 7, 8), (7, 4, 3)]
Resultant tuple list : [1, 4, 3]

Time complexity: O(n), where n is the length of the input list.
Auxiliary space: O(n), which is the space required to store the numpy array created from the input list.

Method #4 : Using list slicing

• Initialize an empty list “res” to store the result.
• Initialize “K” to the required value.
• Iterate over the range from 0 to the length of the “test_list” minus K.
• Within the loop, use list slicing to get the Kth column from the current tuple and the next tuple, and then calculate the absolute difference between them using abs() function.
• Append the difference to the “res” list.
• Return the “res” list as the result.

Python3

# Python3 code to demonstrate working of
# Consecutive Kth column Difference in Tuple List
# Using list slicing

# initializing list
test_list = [(5, 4, 2), (1, 3, 4), (5, 7, 8), (7, 4, 3)]

# printing original list
print("The original list is : " + str(test_list))

# initializing K
K = 1

# using list slicing to get Kth column difference
res = [abs(test_list[i][K] - test_list[i+1][K]) for i in range(len(test_list)-K)]

# printing result
print("Resultant tuple list : " + str(res))

Output

The original list is : [(5, 4, 2), (1, 3, 4), (5, 7, 8), (7, 4, 3)]
Resultant tuple list : [1, 4, 3]

Time complexity: O(n), where n is the length of the “test_list”.
Auxiliary space: O(n), where n is the length of the “test_list”.