Given a list (may contain either strings or numbers), the task is to split the list by some value into two lists.
The approach is very simple. Split the first half of list by given value, and second half from the same value. There are multiple variations possible from this operation based on the requirement, like dropping the first/some element(s) in second half after the split value etc. Let’s see the different ways we can do this task.
Method #1: Using list index
Python3
# Python code to split the list # by some value into two lists.# List initialisationlist = ['Geeks', 'forLazyroar', 'is a', 'portal', 'for Geeks']# Splitting list into first halffirst_list = list[:list.index('forLazyroar')]# Splitting list into second halfsecond_list = list[list.index('forLazyroar')+1:]# Printing first listprint(first_list)# Printing second listprint(second_list) |
['Geeks'] ['is a', 'portal', 'for Geeks']
Time Complexity: O(n), where n is the length of the list test_list
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the res list
Method #2: Using dropwhile and set
Python3
# Python code to split the list # by some value into two lists.# Importingfrom itertools import dropwhile# List initialisationlst = ['Geeks', 'forLazyroar', 'is a', 'portal', 'for Geeks']# Using dropwhile to split into second listsecond_list = list(dropwhile(lambda x: x != 'forLazyroar', lst))[1:]# Using set to get difference between two listsfirst_list = set(lst)-set(second_list)# removing 'split' stringfirst_list.remove('forLazyroar')# converting to listfirst_list = list(first_list)# Printing first listprint(first_list)# Printing second listprint(second_list) |
['Geeks'] ['is a', 'portal', 'for Geeks']
Method 3: Using the itertools.takewhile() and itertools.dropwhile() functions to split the list into two parts based on a condition.
Step-by-step approach:
- Import the itertools module.
- Define the original list to be split.
- Define a lambda function to be used as the condition for takewhile() and dropwhile().
- Use takewhile() to take elements from the list while the condition is true, and store them in a new list.
- Use dropwhile() to drop elements from the list while the condition is true, and store the remaining elements in a new list.
- Remove the first element of the second list, as it is the value that caused the splitting.
- Print the two parts of the original list.
Below is the implementation of the above approach:
Python
import itertools# List initializationmy_list = ['Geeks', 'forLazyroar', 'is a', 'portal', 'for Geeks']# Splitting the list into two partscondition = lambda x: x != 'forLazyroar'first_list = list(itertools.takewhile(condition, my_list))second_list = list(itertools.dropwhile(condition, my_list))[1:]# Printing the two parts of the listprint(first_list)print(second_list) |
['Geeks'] ['is a', 'portal', 'for Geeks']
Time complexity: O(n), where n is the length of the list.
Auxiliary space: O(n), as we create two new lists to store the split parts of the original list.
