Given a list. The task is to convert it to a dictionary with the values as the list element and keys as the concatenation of the given string K and value.
Examples:
Input : test_list = [“gfg”, “is”, “best”], K = “pref_”
Output : {‘pref_gfg’: ‘gfg’, ‘pref_is’: ‘is’, ‘pref_best’: ‘best’}
Explanation : Keys constructed after concatenating K.Input : test_list = [“gfg”, “best”], K = “pref_”
Output : {‘pref_gfg’: ‘gfg’, ‘pref_best’: ‘best’}
Explanation : Keys constructed after concatenating K.
Method #1: Using loop
This is one of the ways in which this task can be performed. In this, we perform concatenation using + operator to construct keys and values are extracted from list.
Python3
# Python3 code to demonstrate working of# Values derived Dictionary keys# Using loop# initializing listtest_list = ["gfg", "is", "best"]# printing original listprint("The original list is : " + str(test_list))# initializing KK = "def_key_"# using loop to construct new Dictionary# + operator used to concat default key and valuesres = dict()for ele in test_list: res[K + str(ele)] = ele# printing resultprint("The constructed Dictionary : " + str(res)) |
Output:
The original list is : [‘gfg’, ‘is’, ‘best’] The constructed Dictionary : {‘def_key_gfg’: ‘gfg’, ‘def_key_is’: ‘is’, ‘def_key_best’: ‘best’}
Time Complexity: O(n) where n is the number of elements in the list “test_list”.
Auxiliary Space: O(n) additional space of size n is created
Method #2: Using dictionary comprehension
This is yet another way in which this task can be performed. In this, we construct a dictionary using one-liner using dictionary comprehension.
Python3
# Python3 code to demonstrate working of# Values derived Dictionary keys# Using dictionary comprehension# initializing listtest_list = ["gfg", "is", "best"]# printing original listprint("The original list is : " + str(test_list))# initializing KK = "def_key_"# using dictionary comprehension# + operator used to concat default key and valuesres = {K + str(ele) : ele for ele in test_list}# printing resultprint("The constructed Dictionary : " + str(res)) |
Output:
The original list is : [‘gfg’, ‘is’, ‘best’] The constructed Dictionary : {‘def_key_gfg’: ‘gfg’, ‘def_key_is’: ‘is’, ‘def_key_best’: ‘best’}
Method #3: Using dict.fromkeys:
Python3
test_list = ["gfg", "is", "best"] # printing original listprint("The original list is : " + str(test_list))K = "def_key_"res = dict.fromkeys(test_list, K)res = {key: K + key for key in res}print("The constructed Dictionary : ", res)#This code is contributed by Jyothi pinjala |
The original list is : ['gfg', 'is', 'best']
The constructed Dictionary : {'gfg': 'def_key_gfg', 'is': 'def_key_is', 'best': 'def_key_best'}
Time Complexity: O(N)
Auxiliary Space: O(N)
Method 4: Use the built-in zip function along with a list comprehension.
Step-by-step approach:
- Initialize two lists: one with the keys (test_list) and another with the corresponding values (each value being the concatenation of “def_key_” and the corresponding key).
- Use the zip function to create a list of tuples where each tuple contains a key-value pair.
- Use a list comprehension to create a dictionary from the list of tuples.
- Return the resulting dictionary.
Python3
test_list = ["gfg", "is", "best"] print("The original list is : " + str(test_list))# Method 4: Using zip and list comprehensionprefix = "def_key_"keys = test_listvalues = [prefix + key for key in keys]res = dict(zip(keys, values))print("The constructed Dictionary : ", res) |
The original list is : ['gfg', 'is', 'best']
The constructed Dictionary : {'gfg': 'def_key_gfg', 'is': 'def_key_is', 'best': 'def_key_best'}
Time complexity: O(n), where n is the length of the input list.
Auxiliary space: O(n), since we create two additional lists (keys and values) that are of the same size as the input list.
