Python program to find Maximum value from dictionary whose key is present in the list

Given a list with dictionary keys and a dictionary, extract maximum from dictionary values, whose key is present in list.

Examples:

Input : test_dict = {“Gfg”: 4, “is” : 5, “best” : 10, “for” : 11, “geeks” : 3}, test_list = [“Gfg”, “best”, “geeks”] 
Output : 10 
Explanation : Max value is 11, but not present in list, 10 is of key best, which is also in list.

Input : test_dict = {“Gfg”: 4, “is” : 5, “best” : 10, “for” : 11, “geeks” : 3}, test_list = [“Gfg”, “best”, “geeks”, “for”] 
Output : 11 
Explanation : Max. value, 11, present in list as well. 

Maximum value from dictionary Using loop

This is one of the ways in which this task can be performed. In this, we check for all the keys present in list and also maximum, then return the maximum available.

Python3

# Python3 code to demonstrate working of
# Maximum value from List keys
# Using loop

# initializing dictionary
test_dict = {"Gfg": 4, "is" : 5, "best" : 9,
             "for" : 11, "geeks" : 3}

# printing original dictionary
print("The original dictionary is : " + str(test_dict))

# initializing list
test_list = ["Gfg", "best", "geeks"]

res = 0
for ele in test_list:

    # checking for key in dictionary
    if ele in test_dict:
        res = max(res, test_dict[ele])

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

Output

The original dictionary is : {'Gfg': 4, 'is': 5, 'best': 9, 'for': 11, 'geeks': 3}
The required maximum : 9

Time complexity: O(n), where n is the number of elements in the test_list. The time complexity is O(n) because it loops through the test_list once and checks for each element if it exists in the test_dict using the in operator, which takes O(1) time on average.
Auxiliary Space: O(1), as it only uses a variable ‘res’ to store the maximum value and it does not increase with the size of the input.

Maximum value from dictionary Using max() + list comprehension

This is yet another way in which this task can be performed. In this, we extract maximum using max() and shorthand list comprehension is used to iterate through values.

Python3

# Python3 code to demonstrate working of
# Maximum value from List keys
# Using max() + list comprehension

# initializing dictionary
test_dict = {"Gfg": 4, "is" : 5, "best" : 9,
             "for" : 11, "geeks" : 3}

# printing original dictionary
print("The original dictionary is : " + str(test_dict))

# initializing list
test_list = ["Gfg", "best", "geeks"]

# maximum is 11, but not present in list,
# hence 9 is output.
res = max([test_dict[ele] for ele in test_list
           if ele in test_dict])

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

Output

The original dictionary is : {'Gfg': 4, 'is': 5, 'best': 9, 'for': 11, 'geeks': 3}
The required maximum : 9

Time complexity: O(n), where n is the number of elements in the test_list. The time complexity is O(n) because the list comprehension will loop through the test_list once and check for each element if it exists in the test_dict using the in operator, which takes O(1) time on average. Then, it takes O(n) time to find the maximum value of the list comprehension.
Auxiliary Space: O(n), as the list comprehension will create a new list of the values of the test_dict keys that are present in test_list, which will take up O(n) space.

Maximum value from dictionary Using Counter() function

Python3

# Python3 code to demonstrate working of
# Maximum value from List keys
from collections import Counter
# initializing dictionary
test_dict = {"Gfg": 4, "is": 5, "best": 9,
             "for": 11, "geeks": 3}

# printing original dictionary
print("The original dictionary is : " + str(test_dict))

# initializing list
test_list = ["Gfg", "best", "geeks"]
freq = Counter(test_list)
res = 0
for ele in test_dict:
    if ele in freq.keys():
        res = max(res, test_dict[ele])

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

Output

The original dictionary is : {'Gfg': 4, 'is': 5, 'best': 9, 'for': 11, 'geeks': 3}
The required maximum : 9

Time Complexity: O(N)
Auxiliary Space: O(N)

Maximum value from dictionary Using reduce() method.

Python3

#Python3 code to demonstrate working of
#Maximum value from List keys
#Using reduce
#importing reduce
from functools import reduce

#initializing dictionary
test_dict = {"Gfg": 4, "is" : 5, "best" : 9,
"for" : 11, "geeks" : 3}

#printing original dictionary
print("The original dictionary is : " + str(test_dict))

#initializing list
test_list = ["Gfg", "best", "geeks"]

#Using reduce() + lambda
res = reduce(lambda x, y: max(x, test_dict[y]), test_list, 0)

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

#this code contributed by tvsk

Output

The original dictionary is : {'Gfg': 4, 'is': 5, 'best': 9, 'for': 11, 'geeks': 3}
The required maximum : 9

Time Complexity: O(n)
Auxiliary Space: O(n)

Maximum value from dictionary Using map() and lambda function

Step-by-step approach:

• Initialize a dictionary test_dict.
• Initialize a list test_list.
• Use map() function to map the keys from the test_list to their corresponding values in the test_dict.
• Use lambda function to return the value of the key passed as an argument.
• Use max() function to get the maximum value from the list generated by map() function.
• Print the result.

Python3

# Python3 code to demonstrate working of
# Maximum value from List keys
# Using map() and lambda function

# initializing dictionary
test_dict = {"Gfg": 4, "is" : 5, "best" : 9,
             "for" : 11, "geeks" : 3}

# printing original dictionary
print("The original dictionary is : " + str(test_dict))

# initializing list
test_list = ["Gfg", "best", "geeks"]

# using map() and lambda function to get the maximum value
res = max(map(lambda x: test_dict[x], test_list))

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

Output

The original dictionary is : {'Gfg': 4, 'is': 5, 'best': 9, 'for': 11, 'geeks': 3}
The required maximum : 9

Time complexity: O(n), where n is the number of keys in the list test_list.
Auxiliary space: O(1), as only constant extra space is used.

Maximum value from dictionary Using the sorted() function

Step-by-step approach:

• Sort the list in descending order based on the values of the keys in the dictionary
• Get the first element of the sorted list, which will have the maximum value
• This method assumes that the keys in the list are present in the dictionary

Below is the implementation of the above approach:

Python3

# Python3 code to demonstrate working of
# Maximum value from List keys
# Using sorted() function

# initializing dictionary
test_dict = {"Gfg": 4, "is" : 5, "best" : 9,
             "for" : 11, "geeks" : 3}

# printing original dictionary
print("The original dictionary is : " + str(test_dict))

# initializing list
test_list = ["Gfg", "best", "geeks"]

# using sorted() function to get the maximum value
sorted_list = sorted(test_list, key=lambda x: test_dict[x], reverse=True)
res = test_dict[sorted_list[0]]

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

Output

The original dictionary is : {'Gfg': 4, 'is': 5, 'best': 9, 'for': 11, 'geeks': 3}
The required maximum : 9

Time complexity: O(n log n), where n is the length of the list.
Auxiliary space: O(n), where n is the length of the list.