Python – Unique Values of Key in Dictionary

Sometimes, while working with Python dictionaries, we can have a problem in which we need to extract the unique values of a particular key in Dictionary List. This kind of problem in very common in day-day programming and web development domain. Lets discuss certain ways in which this task can be performed.

Input : test_list = [{‘geeks’: 10, ‘for’: 8, ‘best’: 10}, {‘best’: 10}]
Output : [10]

Input : test_list = [{‘best’: 11}]
Output : [11]

Method #1 : Using loop + set()
The combination of above functions can be used to solve this problem. In this, we extract all the elements of key in loop and then convert the extracted list to set to get unique values.

# Python3 code to demonstrate working of
# Unique Values of Key in Dictionary
# Using loop + set()

# initializing list
test_list = [{'Gfg' : 5, 'is' : 6, 'best' : 7, 'for' : 8, 'geeks' : 10},
             {'Gfg' : 9, 'is' : 4, 'best' : 7, 'for' : 4, 'geeks' :7},
             {'Gfg' : 2, 'is' : 10, 'best' : 8, 'for' : 9, 'geeks' : 3}]

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

# initializing key
op_key = 'best'

# Unique Values of Key in Dictionary
# Using loop + set()
res = []
for sub in test_list:
    res.append(sub[op_key])
res = list(set(res))

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

Output :

The original list is : [{‘for’: 8, ‘best’: 7, ‘is’: 6, ‘Gfg’: 5, ‘geeks’: 10}, {‘for’: 4, ‘best’: 7, ‘is’: 4, ‘Gfg’: 9, ‘geeks’: 7}, {‘for’: 9, ‘best’: 8, ‘is’: 10, ‘Gfg’: 2, ‘geeks’: 3}]
The unique values of key : [8, 7]

Method #2 : Using list comprehension
This is yet another way to solve this problem. In this, we perform in a similar way as above method but in a shorthand approach.

# Python3 code to demonstrate working of
# Unique Values of Key in Dictionary
# Using list comprehension

# initializing list
test_list = [{'Gfg' : 5, 'is' : 6, 'best' : 7, 'for' : 8, 'geeks' : 10},
             {'Gfg' : 9, 'is' : 4, 'best' : 7, 'for' : 4, 'geeks' :7},
             {'Gfg' : 2, 'is' : 10, 'best' : 8, 'for' : 9, 'geeks' : 3}]

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

# initializing key
op_key = 'best'

# Unique Values of Key in Dictionary
# Using list comprehension
res = list(set(sub[op_key] for sub in test_list))

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

Output :

The original list is : [{‘for’: 8, ‘best’: 7, ‘is’: 6, ‘Gfg’: 5, ‘geeks’: 10}, {‘for’: 4, ‘best’: 7, ‘is’: 4, ‘Gfg’: 9, ‘geeks’: 7}, {‘for’: 9, ‘best’: 8, ‘is’: 10, ‘Gfg’: 2, ‘geeks’: 3}]
The unique values of key : [8, 7]