Python – Extract Unique value key pairs

Sometimes, while working on Python dictionaries, we can have a problem in which we need to perform the extraction of selected pairs of keys from dictionary list, that too unique. This kind of problem can have application in many domains including day-day programming. Let’s discuss certain ways in which this task can be performed.

Input : test_list = [{‘gfg’ : 5, ‘best’ : 12}, {‘gfg’ : 5, ‘best’ : 12}, ] 
Output : {(5, 12)} 

Input : test_list = [{‘gfg’ : 5, ‘is’: 5, ‘best’ : 12}] 
Output : {(5, 12)}

Method #1 : Using list comprehension This problem can be solved using above functionality. In this, we perform the match, using conditionals and “in” operator. The whole logic compiled using list comprehension. 

Python3

# Python3 code to demonstrate working of
# Extract Unique value key pairs
# Using list comprehension

# initializing list
test_list = [{'gfg' : 5, 'is' : 8, 'best' : 12},
             {'gfg' : 5, 'is' : 12, 'best' : 12},
             {'gfg' : 20, 'is' : 17, 'best' : 12}]

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

# initializing required keys
req_key1 = 'gfg'
req_key2 = 'best'

# Extract Unique value key pairs
# Using list comprehension
res =  {tuple(sub[idx] for idx in [req_key1, req_key2]) for sub in test_list}

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

Output : 

The original list is : [{‘gfg’: 5, ‘is’: 8, ‘best’: 12}, {‘gfg’: 5, ‘is’: 12, ‘best’: 12}, {‘gfg’: 20, ‘is’: 17, ‘best’: 12}] The required values : {(5, 12), (20, 12)}

Time complexity: O(n), where n is the number of dictionaries in the test_list. The code iterates over each dictionary once.
Auxiliary Space: O(n), where n is the number of dictionaries in the test_list. The space used by the res set is proportional to the number of dictionaries in test_list.

Method #2 : Using map() + zip() + itemgetter() The combination of above functionalities can be used to perform this task. In this, we use itemgetter to extract the values, zip() is used to combine values, and map() is used to convert the combined result to set. 

Python3

# Python3 code to demonstrate working of
# Extract Unique value key pairs
# Using map() + zip() + itemgetter()
from operator import itemgetter

# initializing list
test_list = [{'gfg' : 5, 'is' : 8, 'best' : 12},
             {'gfg' : 5, 'is' : 12, 'best' : 12},
             {'gfg' : 15, 'is' : 17, 'best' : 21}]

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

# initializing required keys
req_key1 = 'gfg'
req_key2 = 'best'

# Extract Unique value key pairs
# Using map() + zip() + itemgetter()
temp = zip(*map(itemgetter(req_key1, req_key2), test_list))
res = list(map(set, temp))

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

Output : 

The original list is : [{‘gfg’: 5, ‘is’: 8, ‘best’: 12}, {‘gfg’: 5, ‘is’: 12, ‘best’: 12}, {‘gfg’: 15, ‘is’: 17, ‘best’: 21}] The required values : [{5, 15}, {12, 21}]

Time complexity :- O(N)

Space complexity :- O(1)

Method #3: Using a for loop and a set

use a for loop and a set to extract unique key-value pairs from the input list.

Python3

# Python3 code to demonstrate working of
# Extract Unique value key pairs
# Using a for loop and a set

# initializing list
test_list = [{'gfg' : 5, 'is' : 8, 'best' : 12},
             {'gfg' : 5, 'is' : 12, 'best' : 12},
             {'gfg' : 20, 'is' : 17, 'best' : 12}]

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

# initializing required keys
req_key1 = 'gfg'
req_key2 = 'best'

# Extract Unique value key pairs
# Using a for loop and a set
res_set = set()
for sub in test_list:
    res_set.add((sub[req_key1], sub[req_key2]))
res = list(res_set)

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

Output

The original list is : [{'gfg': 5, 'is': 8, 'best': 12}, {'gfg': 5, 'is': 12, 'best': 12}, {'gfg': 20, 'is': 17, 'best': 12}]
The required values : [(5, 12), (20, 12)]

Time complexity: O(n), where n is the number of elements in the input list.
Space complexity: O(n), where n is the number of unique key-value pairs.

Method #4: Using dictionary comprehension and set conversion

1. Initialize an empty dictionary and set.
2. Use dictionary comprehension to iterate over each dictionary in the list, get the values for the required keys, and add them as key-value pairs to the dictionary. Since the keys of a dictionary are unique, this will automatically remove any duplicates.
3. Convert the keys of the dictionary to a set to remove duplicates.
4. Convert the set to a list to get the final result. 

Python3

test_list = [{'gfg' : 5, 'is' : 8, 'best' : 12},              {'gfg' : 5, 'is' : 12, 'best' : 12},             {'gfg' : 20, 'is' : 17, 'best' : 12}]

req_key1 = 'gfg'
req_key2 = 'best'

result_dict = {(d[req_key1], d[req_key2]): None for d in test_list}
result_set = set(result_dict.keys())
result = list(result_set)

print("The required values : " + str(result))

Output

The required values : [(5, 12), (20, 12)]

Time complexity: O(n), where n is the length of the input list.
Auxiliary space: O(n) for the dictionary and set.