The concept of dictionary is similar to that of map data structure in C++ language, but with the exception that keys in dictionary has nothing to do with its ordering, i.e it is not sorted unlike C++ in which the keys are sorted internally. This opens up the problem in which we might have to find the exact position of key in the dictionary. Let’s discuss certain ways in which this task can be performed.
Method #1 : Using list comprehension + enumerate() The combination of above functions together can perform this particular task. In this, first the dictionary is converted to a pair tuple and then the first element of tuple being the key is checked for index.
Python3
# Python3 code to demonstrate working of# Key index in Dictionary# Using list comprehension + enumerate()# initializing dictionarytest_dict = {'all' : 1, 'food' : 2, 'good' : 3, 'have' : 4}# initializing search key stringsearch_key = 'good'# printing original dictionaryprint("The original dictionary is : " + str(test_dict))# Using list comprehension + enumerate()# Key index in Dictionarytemp = list(test_dict.items())res = [idx for idx, key in enumerate(temp) if key[0] == search_key]# printing resultprint("Index of search key is : " + str(res)) |
The original dictionary is : {'have': 4, 'all': 1, 'good': 3, 'food': 2}
Index of search key is : [2]
Time complexity: O(n*n), where n is the number of key-value pairs in the dictionary.
Auxiliary space: O(n), to store the keys and values in dictionary.
Method #2 : Using list() + keys() + index() The combination of above functions can also be used to perform this particular task. In this, the dictionary keys are first converted to list and then found the desired one using the index method.
Python3
# Python3 code to demonstrate working of# Key index in Dictionary# Using list() + keys() + index()# initializing dictionarytest_dict = {'all' : 1, 'food' : 2, 'good' : 3, 'have' : 4}# initializing search key stringsearch_key = 'good'# printing original dictionaryprint("The original dictionary is : " + str(test_dict))# Using list() + keys() + index()# Key index in Dictionaryres = list(test_dict.keys()).index(search_key)# printing resultprint("Index of search key is : " + str(res)) |
The original dictionary is : {'food': 2, 'have': 4, 'good': 3, 'all': 1}
Index of search key is : 2
Method#3: for loop
Approach
uses a for loop to iterate through the keys of the dictionary and find the index of the search key.
Algorithm
1. Create a dictionary dict1 with key-value pairs.
2. Initialize the search key and index to None.
3. Iterate through the dictionary to find the index of the search key using a for loop.
4. When the search key is found, assign the index to a variable and break the loop.
5. Print the index of the search key.
Python3
# initialize dictionarydict1 = {'have': 4, 'all': 1, 'good': 3, 'food': 2}# initialize search key and indexsearch_key = 'good'index = None# iterate through the dictionary to find the index of the search keyfor i, key in enumerate(dict1.keys()): if key == search_key: index = i breakprint("Index of search key is : {}".format([index])) |
Index of search key is : [2]
Time Complexity: O(n), where n is the number of elements in the dictionary.
Auxiliary Space: O(1), as we are not using any extra memory.
