Python | Swap tuple elements in list of tuples

While doing competitive programming, one can come across a question in which one requires to work with 2D plane and work with coordinates. One such subproblem can be swapping x, y coordinate elements. Let’s discuss certain ways in which this problem can be solved using tuple element swapping. 

Method #1 : Using list comprehension This is just a brute method to perform the longer method of loop for swapping the elements. In this a new list of tuple is created rather than an inplace swap. 

Python3

# Python3 code to demonstrate working of
# Swap tuple elements in list of tuples
# Using list comprehension

# initializing list
test_list = [(3, 4), (6, 5), (7, 8)]

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

# Swap tuple elements in list of tuples
# Using list comprehension
res = [(sub[1], sub[0]) for sub in test_list]

# printing result
print("The swapped tuple list is : " + str(res))

Output : 

The original list is : [(3, 4), (6, 5), (7, 8)]
The swapped tuple list is : [(4, 3), (5, 6), (8, 7)]

Time Complexity: O(n) where n is the number of elements in the list “test_list”.  
Auxiliary Space: O(n), where n is the number of elements in the new res list 

Method #2 : Using map() + lambda Yet another way to perform this task is using map and lambda. This is a bit slower in execution but a more compact way to perform this task. 

Python3

# Python3 code to demonstrate working of
# Swap tuple elements in list of tuples
# Using map() + lambda

# initializing list
test_list = [(3, 4), (6, 5), (7, 8)]

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

# Swap tuple elements in list of tuples
# Using map() + lambda
res = list(map(lambda sub: (sub[1], sub[0]), test_list))

# printing result
print("The swapped tuple list is : " + str(res))

Output : 

The original list is : [(3, 4), (6, 5), (7, 8)]
The swapped tuple list is : [(4, 3), (5, 6), (8, 7)]

Time Complexity: O(n) where n is the number of elements in the list “res_list”.  
Auxiliary Space: O(n), where n is the number of elements in the new res list 

Method #3 : Using list(),reverse() and tuple() methods

1. Initiated a for loop to traverse the list
2. Converted each  tuple to list and used reverse() to swap elements
3. Converted the list again to tuple and appended to output list
4. Displayed the output list

Python3

# Python3 code to demonstrate working of
# Swap tuple elements in list of tuples

# initializing list
test_list = [(3, 4), (6, 5), (7, 8)]

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

# Swap tuple elements in list of tuples
# Using list comprehension
res=[]
for i in test_list:
    x=list(i)
    x.reverse()
    res.append(tuple(x))

# printing result
print("The swapped tuple list is : " + str(res))

Output

The original list is : [(3, 4), (6, 5), (7, 8)]
The swapped tuple list is : [(4, 3), (5, 6), (8, 7)]

Time Complexity: O(n)
Auxiliary Space: O(n)

Method 4: using a simple for loop:

Python3

# Python3 code to demonstrate working of
# Swap tuple elements in list of tuples

# initializing list
test_list = [(3, 4), (6, 5), (7, 8)]

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

# Swap tuple elements in list of tuples
# Using for loop
res = []
for i in test_list:
    x, y = i
    res.append((y, x))

# printing result
print("The swapped tuple list is : " + str(res))

Output

The original list is : [(3, 4), (6, 5), (7, 8)]
The swapped tuple list is : [(4, 3), (5, 6), (8, 7)]

Time complexity: O(n), where n is the number of tuples in the list,
Auxiliary space: O(n) because we are creating a new list of the same length as the original list.