Python – Extract elements from Ranges in List

Given a list, and a list of tuples with ranges, extract all elements in those ranges from list.

Input : test_list = [4, 5, 4, 6, 7, 5, 4, 5, 6, 10], range_list = [(2, 4), (7, 8)] 
Output : [4, 6, 7, 5, 6] 
Explanation : 4, 6, 7 are elements at idx 2, 3, 4 and 5, 6 at idx 7, 8. 

Input : test_list = [4, 5, 4, 6, 7, 5, 4, 5, 6, 10], range_list = [(2, 6)] 
Output : [4, 6, 7, 5, 4] 
Explanation : Elements from 2-6 index are extracted.

Method #1 : Using loop + list slicing 

In this, we extract each range using list slicing and using loop iterate for each range and keep extending the extracting slices to extending list.

Python3

# Python3 code to demonstrate working of
# Extract elements from Ranges in List
# Using loop + list slicing

# initializing list
test_list = [4, 5, 4, 6, 7, 5, 4, 5, 4, 6, 4, 6, 9, 8]

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

# initializing ranges
range_list = [(2, 4), (7, 8), (10, 12)]

res = []
for ele in range_list:

    # extending ranges
    res.extend(test_list[ele[0] : ele[1] + 1])

# printing result
print("Ranges elements : " + str(res))

Output

The original list is : [4, 5, 4, 6, 7, 5, 4, 5, 4, 6, 4, 6, 9, 8]
Ranges elements : [4, 6, 7, 5, 4, 4, 6, 9]

Time Complexity: O(n), where n is the length of the input list. 
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the list “test_list”. 

Method #2: Using list comprehension

In this, we apply similar method as above function, difference being that list comprehension is used to solve this in compact form.

Python3

# Python3 code to demonstrate working of
# Extract elements from Ranges in List
# Using list comprehension
from itertools import chain

# initializing list
test_list = [4, 5, 4, 6, 7, 5, 4, 5, 4, 6, 4, 6, 9, 8]

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

# initializing ranges
range_list = [(2, 4), (7, 8), (10, 12)]

# using one-liner to solve this problem
res = list(chain.from_iterable([test_list[ele[0] : ele[1] + 1] for ele in range_list]))

# printing result
print("Ranges elements : " + str(res))

Output

The original list is : [4, 5, 4, 6, 7, 5, 4, 5, 4, 6, 4, 6, 9, 8]
Ranges elements : [4, 6, 7, 5, 4, 4, 6, 9]

Method 3 : Using map() and lambda function

Python3

# Python3 code to demonstrate working of
# Extract elements from Ranges in List
# Using map() and lambda function

# initializing list
test_list = [4, 5, 4, 6, 7, 5, 4, 5, 4, 6, 4, 6, 9, 8]

# initializing ranges
range_list = [(2, 4), (7, 8), (10, 12)]

# using map() and lambda function to solve this problem
res = list(map(lambda x: test_list[x[0]:x[1]+1], range_list))

# using chain() to flatten the list of lists
from itertools import chain
res = list(chain(*res))

# printing result
print("Ranges elements : " + str(res))

Output

Ranges elements : [4, 6, 7, 5, 4, 4, 6, 9]

Time Complexity: O(n * m), where n is the length of the test_list and m is the number of ranges in range_list.
Auxiliary Space: O(k), where k is the total number of elements in the ranges in range_list.