Python – Tuple key detection from value list

Sometimes, while working with record data, we can have a problem in which we need to extract the key which has matching value of K from its value list. This kind of problem can occur in domains that are linked to data. Lets discuss certain ways in which this task can be performed.

Method #1 : Using List comprehension
This task can be performed using List comprehension. In this, we iterate through each records and test it’s value list for K. If found we return that key.

Python3

# Python3 code to demonstrate
# Tuple key detection from value list
# using List comprehension

# Initializing list
test_list = [('Gfg', [1, 3, 4]), ('is', [5, 8, 10]), ('best', [11, 9, 2])]

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

# Initializing K
K = 4

# Tuple key detection from value list
# using List comprehension
res = [sub[0] for sub in test_list if K in sub[1]]

# printing result
print ("The required key of list values : " + str(res))

Output : 

The original list is : [('Gfg', [1, 3, 4]), ('is', [5, 8, 10]), ('best', [11, 9, 2])]
The required key of list values : ['Gfg']

Method #2 : Using filter() + lambda
The combination of above functions can also be used to perform this task. In this, filter() is used to check for existence in list and extract the required key with help of lambda.

Python3

# Python3 code to demonstrate
# Tuple key detection from value list
# using filter() + lambda

# Initializing list
test_list = [('Gfg', [1, 3, 4]), ('is', [5, 8, 10]), ('best', [11, 9, 2])]

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

# Initializing K
K = 4

# Tuple key detection from value list
# using filter() + lambda
res = list(filter(lambda sub, ele = K : ele in sub[1], test_list))

# printing result
print ("The required key of list values : " + str(res[0][0]))

Output : 

The original list is : [('Gfg', [1, 3, 4]), ('is', [5, 8, 10]), ('best', [11, 9, 2])]
The required key of list values : Gfg

Method 3: Using a for loop
This approach uses a for loop to iterate through the elements in the list and check if the value of K is present in the second element of each tuple. If it is found, we break the loop and return the first element of the tuple.

Python3

# Python3 code to demonstrate
# Tuple key detection from value list
# using a for loop

# Initializing list
test_list = [('Gfg', [1, 3, 4]), ('is', [5, 8, 10]), ('best', [11, 9, 2])]

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

# Initializing K
K = 4

# Tuple key detection from value list using a for loop
for sub in test_list:
    if K in sub[1]:
        res = sub[0]
        break

# printing result
print ("The required key of list values : " + str(res))
#This code is contributed by Edula Vinay Kumar Reddy

Output

The original list is : [('Gfg', [1, 3, 4]), ('is', [5, 8, 10]), ('best', [11, 9, 2])]
The required key of list values : Gfg

Time Complexity: O(n), where n is the number of elements in the list. The for loop runs n times, and the in operator has a time complexity of O(k), where k is the length of the list in the second element of the tuple.
Auxiliary Space: O(1), as we only use a few variables.

Method 4 : using the built-in function any() with a generator expression

Step-by-step approach:

1. Initialize the input list of tuples and print it.
2. Initialize the target value K and print it.
3. Use any() with a generator expression to check if any of the tuples contains the value K. If so, store the corresponding key in a variable res.
4. Print the result.

Python3

# Initializing list
test_list = [('Gfg', [1, 3, 4]), ('is', [5, 8, 10]), ('best', [11, 9, 2])]
# printing original list
print("The original list is : " + str(test_list))

# Initializing K
K = 4
# printing target value
print("The target value is : " + str(K))

# Tuple key detection from value list using any() with generator expression
res = next((sub[0] for sub in test_list if K in sub[1]), None)

# printing result
print ("The required key of list values : " + str(res))

Output

The original list is : [('Gfg', [1, 3, 4]), ('is', [5, 8, 10]), ('best', [11, 9, 2])]
The target value is : 4
The required key of list values : Gfg

Time complexity: O(n) in the worst case, where n is the length of the input list. 
Auxiliary space: O(1) because we only need to store a few variables (test_list, K, res) regardless of the input size. 

Method 5: Using a dictionary

Step-by-step approach:

• Initialize an empty dictionary value_to_key_dict.
• Loop through each element of the test_list using a for loop.
• Within the loop, loop through the sublist and map each value to its corresponding key in the original list by adding an entry to value_to_key_dict with the value as the key and the corresponding key from the original list as the value.
• Use the get method of the dictionary to check if K exists in the keys of value_to_key_dict. If it does, return the corresponding value from the dictionary, which will be the key from the original list.
• If K is not found, return None.
• Print the result.

Python3

# Initializing list
test_list = [('Gfg', [1, 3, 4]), ('is', [5, 8, 10]), ('best', [11, 9, 2])]
# printing original list
print("The original list is : " + str(test_list))

# Initializing K
K = 4
# printing target value
print("The target value is : " + str(K))

# Using a dictionary to map values to keys
value_to_key_dict = {}
for key, value_list in test_list:
    for value in value_list:
        value_to_key_dict[value] = key

# Check if K exists in the keys of the dictionary
res = value_to_key_dict.get(K)

# printing result
print ("The required key of list values : " + str(res))

Output

The original list is : [('Gfg', [1, 3, 4]), ('is', [5, 8, 10]), ('best', [11, 9, 2])]
The target value is : 4
The required key of list values : Gfg

Time complexity: O(n*m), where n is the length of the original list and m is the maximum length of the sublists. 
Auxiliary space: O(n*m), where n and m are as defined above, because we need to store each value and its corresponding key in the dictionary.