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.

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.
 

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

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:

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:

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

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.

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)