Python - Test Record existence in Dictionary

Sometimes while working with a pool of records, we can have problems in which we need to check the presence of a particular value of a key for existence. This can have applications in many domains such as day-day programming or web development. Let us discuss certain ways in which this task can be performed.

Method #1 : Using any() + generator expression 

The combination of the above functions can be used to perform this task. In this, we simply test for all elements using any(), iterated using generator expression.

# Python3 code to demonstrate working of
# Test Record existence in Dictionary
# Using any() + generator expression

# initializing list
test_list = [{'name': 'Nikhil', 'age': 22},
             {'name': 'Akshat', 'age': 23},
             {'name': 'Akash', 'age': 23}]

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

# initializing key and value
test_key = 'name'
test_val = 'Nikhil'

# Test Record existence in Dictionary
# Using any() + generator expression
res = any(sub[test_key] == test_val for sub in test_list)

# printing result
print("Does key value contain in dictionary list : " + str(res))

Time Complexity: O(n) where n is the total number of values in the list “test_list”. 
Auxiliary Space: O(n) where n is the total number of values in the list “test_list”.

Method #2 : Using filter() + lambda 

The combination of the above functions can be used to perform this task. In this, we check for all values using filter and iteration using lambda function.
 

# Python3 code to demonstrate working of
# Test Record existence in Dictionary
# Using filter() + lambda

# initializing list
test_list = [{'name': 'Nikhil', 'age': 22},
             {'name': 'Akshat', 'age': 23},
             {'name': 'Akash', 'age': 23}]


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

# initializing key and value
test_key = 'name'
test_val = 'Nikhil'

# Test Record existence in Dictionary
# Using filter() + lambda
res = filter(lambda sub: test_val in sub.values(), test_list)
if len(list(res)):
    res = True
else:
    res = False

# printing result
print("Does key value contain in dictionary list : " + str(res))

Time Complexity: O(n*n), where n is the length of the input list. This is because we’re using the filter() + lambda which has a time complexity of O(n*n) in the worst case.
Auxiliary Space: O(n), as we’re using additional space res other than the input list itself with the same size of input list.

Method #3 : Using keys() method

# Python3 code to demonstrate working of
# Test Record existence in Dictionary

# initializing list
test_list = [{ 'name' : 'Nikhil', 'age' : 22},
            { 'name' : 'Akshat', 'age' : 23},
            { 'name' : 'Akash', 'age' : 23}]


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

# initializing key and value
test_key = 'name'
test_val = 'Nikhil'

# Test Record existence in Dictionary
res=False
for i in test_list:
    if test_key in i.keys() and i[test_key]==test_val:
        res=True
# printing result
print("Does key value contain in dictionary list : " + str(res))

The original list is : [{'name': 'Nikhil', 'age': 22}, {'name': 'Akshat', 'age': 23}, {'name': 'Akash', 'age': 23}]
Does key value contain in dictionary list : True

Time complexity: The time complexity of the given code is O(n), where n is the number of dictionaries in the test_list.

Auxiliary space: The auxiliary space used by the code is also O(1), which is a constant amount of space.

Method 4: Using a list comprehension

Step-by-step approach:

• Initialize the list test_list.
• Print the original list using the print() function.
• Initialize the key-value pair to be searched for.
• Use a list comprehension to generate a list of True and False values based on whether the key-value pair is present in each dictionary in test_list.
• Check if any of the values in the list generated in step 4 are True.
• Print the final result.

Below is the implementation of the above approach:

# Python3 code to demonstrate working of
# Test Record existence in Dictionary

# initializing list
test_list = [{ 'name' : 'Nikhil', 'age' : 22},
            { 'name' : 'Akshat', 'age' : 23},
            { 'name' : 'Akash', 'age' : 23}]


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

# initializing key and value
test_key = 'name'
test_val = 'Nikhil'

# Test Record existence in Dictionary
res = any(i.get(test_key) == test_val for i in test_list)

# printing result
print("Does key value contain in dictionary list : " + str(res))

The original list is : [{'name': 'Nikhil', 'age': 22}, {'name': 'Akshat', 'age': 23}, {'name': 'Akash', 'age': 23}]
Does key value contain in dictionary list : True

Time complexity: O(n), where n is the length of the test_list since we need to iterate over each dictionary in the list once.
Auxiliary space: O(1), since we are only using a constant amount of extra memory to store the key-value pair to be searched for, the result variable, and the True/False list generated in the list comprehension.

Method #5: Using a for loop

Step-by-step approach:

• Two variables test_key and test_val are initialized with the key and value to be searched in the dictionaries.
• A boolean variable res is initialized with False.
• A for loop is used to iterate through each dictionary d in test_list.
  • Inside the for loop, an if condition is used to check if the current dictionary d contains the test_key and its value is equal to test_val.
  • If the above condition is satisfied, the res variable is set to True and the loop is broken using the break statement.
• The value of res is printed using the print() function.

Below is the implementation of the above approach:

# Python3 code to demonstrate working of
# Test Record existence in Dictionary

# initializing list
test_list = [{ 'name' : 'Nikhil', 'age' : 22},
            { 'name' : 'Akshat', 'age' : 23},
            { 'name' : 'Akash', 'age' : 23}]


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

# initializing key and value
test_key = 'name'
test_val = 'Nikhil'

# Test Record existence in Dictionary
res = False
for d in test_list:
    if test_key in d and d[test_key] == test_val:
        res = True
        break

# printing result
print("Does key value contain in dictionary list : " + str(res))

The original list is : [{'name': 'Nikhil', 'age': 22}, {'name': 'Akshat', 'age': 23}, {'name': 'Akash', 'age': 23}]
Does key value contain in dictionary list : True

Time Complexity: O(n), where n is the length of test_list.
Auxiliary Space: O(1), as constant extra space is used.

Method #6: Using reduce():

Algorithm:

• Import the reduce function from functools module.
• Initialize the list of dictionaries.
• Initialize the key and value to search in the list of dictionaries.
• Use the reduce function to iterate over the list of dictionaries and check if the key exists and the value matches the provided value using the lambda function.
• If any dictionary in the list satisfies the condition, return True, else False.
• Print the result

from functools import reduce

# initializing list
test_list = [{'name': 'Nikhil', 'age': 22},
             {'name': 'Akshat', 'age': 23},
             {'name': 'Akash', 'age': 23}]

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

# initializing key and value
test_key = 'name'
test_val = 'Nikhil'

# Test Record existence in Dictionary using reduce()
res = reduce(lambda x, y: x or (test_key in y and y[test_key] == test_val), test_list, False)

# printing result
print("Does key value contain in dictionary list:", res)
#This code is contributed by Pushpa.

The original list is: [{'name': 'Nikhil', 'age': 22}, {'name': 'Akshat', 'age': 23}, {'name': 'Akash', 'age': 23}]
Does key value contain in dictionary list: True

Time complexity: O(n), where n is the length of the list of dictionaries. In the worst case, we may have to check all the dictionaries in the list.
Auxiliary Space: O(1), as we are not using any additional data structures that depend on the size of the input.

Method #7: Using dictionary comprehension

Step-by-step approach:

• Initialize the list of dictionaries called "test_list".
• Print the original list using the "print()" function.
• Initialize the key and value that need to be checked for existence in the dictionaries of the list.
• Use the "any()" function with a generator expression to check if the key-value pair exists in any of the dictionaries in the list.
• Store the result in a variable called "res".
• Print the result using the "print()" function.

# Python3 code to demonstrate working of
# Test Record existence in Dictionary

# initializing list
test_list = [{ 'name' : 'Nikhil', 'age' : 22},
            { 'name' : 'Akshat', 'age' : 23},
            { 'name' : 'Akash', 'age' : 23}]

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

# initializing key and value
test_key = 'name'
test_val = 'Nikhil'

# Test Record existence in Dictionary
res = any(d[test_key] == test_val for d in test_list)

# printing result
print("Does key value contain in dictionary list : " + str(res))

The original list is : [{'name': 'Nikhil', 'age': 22}, {'name': 'Akshat', 'age': 23}, {'name': 'Akash', 'age': 23}]
Does key value contain in dictionary list : True

Time complexity: O(n)
Auxiliary space: O(1)