Python – Maximum String value length of Key

Sometimes, while working with Python dictionaries, we can have a problem in which we need to find the maximum length of all the string values of particular key. This problem can occur in domains of day-day programming and web development. Let’s discuss certain ways in which this task can be performed. 

Examples – 

Input: test_list = [{‘key1’ : “abcd”, ‘key2’ : 2}, {‘key1’ : “qwertyui”, ‘key2’ : 2}, {‘key1’ : “xcvz”, ‘key3’ : 3}, {‘key1’ : None, ‘key3’ : 4}] Output: 8 
Explanation: Among all values for given key key1, qwertyui has maximum length (which is 8).

Method #1 : Using max() + len() + list comprehension The combination of above functions can be used to solve this problem. In this, we compute the maximum string length using max() and len(). The comparison with each is bound by list comprehension. 

Python3

# Python3 code to demonstrate working of
# Maximum String value length of Key
# Using max() + len() + list comprehension

# initializing list
test_list = [{'Gfg' :  "abcd", 'best' : 2},
             {'Gfg' :  "qwertyui", 'best' : 2},
             {'Gfg' :  "xcvz", 'good' : 3},
             {'Gfg' : None, 'good' : 4}]

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

# initializing Key
filt_key = 'Gfg'

# Maximum String value length of Key
# Using max() + len() + list comprehension
temp = (sub[filt_key] for sub in test_list)
res = max(len(ele) for ele in temp if ele is not None)

# printing result
print("The maximum length key value : " + str(res))

Output : 

The original list is : [{‘best’: 2, ‘Gfg’: ‘abcd’}, {‘best’: 2, ‘Gfg’: ‘qwertyui’}, {‘good’: 3, ‘Gfg’: ‘xcvz’}, {‘good’: 4, ‘Gfg’: None}] The maximum length key value : 8

Time complexity: O(N), where N is the length of the input list test_list.
Auxiliary space: O(1), as the program uses constant extra space to store variables like test_list, filt_key, temp, res, etc., and the space required does not depend on the size of the input.

Method #2 : Using list comprehension + len() + max() (one liner) The similar task can also be combined to perform in one line for compact solution. 

Python3

# Python3 code to demonstrate working of
# Maximum String value length of Key
# Using max() + len() + list comprehension (one liner)

# initializing list
test_list = [{'Gfg' :  "abcd", 'best' : 2},
             {'Gfg' :  "qwertyui", 'best' : 2},
             {'Gfg' :  "xcvz", 'good' : 3},
             {'Gfg' : None, 'good' : 4}]

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

# initializing Key
filt_key = 'Gfg'

# Maximum String value length of Key
# Using max() + len() + list comprehension (one liner)
res = len(max(test_list, key = lambda sub: len(sub[filt_key])
                if sub[filt_key] is not None else 0)[filt_key])

# printing result
print("The maximum length key value : " + str(res))

Output : 

The original list is : [{‘best’: 2, ‘Gfg’: ‘abcd’}, {‘best’: 2, ‘Gfg’: ‘qwertyui’}, {‘good’: 3, ‘Gfg’: ‘xcvz’}, {‘good’: 4, ‘Gfg’: None}] The maximum length key value : 8

Time complexity: O(n*n), where n is the number of elements in the test_list.
Auxiliary space: O(1), as program uses the constant space