Python – Merge keys by values
Last Updated :
18 May, 2023
Given a dictionary, merge the keys to map to common values.
Examples:
Input : test_dict = {1:6, 8:1, 9:3, 10:3, 12:6, 4:9, 2:3}
Output : {'1-12': 6, '2-9-10': 3, '4': 9, '8': 1}
Explanation : All the similar valued keys merged.
Input : test_dict = {1:6, 8:1, 9:3, 4:9, 2:3}
Output : {'1': 6, '2-9': 3, '4': 9, '8': 1}
Explanation : All the similar valued keys merged.
Method 1: Using defaultdict() + loop
This task is performed in 2 steps, first, group all the values and storing keys, and in 2nd step, map merged keys to common values.
Python3
from collections import defaultdict
test_dict = {1: 6, 8: 1, 9: 3, 10: 3, 12: 6, 4: 9, 2: 3}
print("The original dictionary is : " + str(test_dict))
temp = defaultdict(list)
for key, val in sorted(test_dict.items()):
temp[val].append(key)
res = dict()
for key in temp:
res['-'.join([str(ele) for ele in temp[key]])] = key
print("The required result : " + str(res))
|
Output:
The original dictionary is : {1: 6, 8: 1, 9: 3, 10: 3, 12: 6, 4: 9, 2: 3}
The required result : {‘1-12’: 6, ‘2-9-10’: 3, ‘4’: 9, ‘8’: 1}
Time Complexity: O(n), where n is the length of the list test_dict
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the res list
Method 2: Using a dictionary to store the merged keys
Approach:
- Create an empty dictionary merged_dict to store the merged keys and values.
- Loop through each key-value pair in the input dictionary test_dict.
- Check if the value already exists in the merged_dict.
- If the value does not exist, create a new key-value pair in the merged_dict with the value as the key and a list containing the key as the value.
- If the value already exists, append the key to the list of keys corresponding to that value in the merged_dict.
- Loop through each key in the merged_dict.
- If the length of the list of keys corresponding to that value is 1, replace the list with a single key.
- If the length of the list of keys corresponding to that value is greater than 1, sort the list of keys in ascending order, join them with a dash (‘-‘), and replace the list with the joined string.
- Return the merged dictionary and print the elements in the dictionary.
Python3
def merge_keys(test_dict):
merged_dict = {}
for key, value in test_dict.items():
if value not in merged_dict:
merged_dict[value] = [key]
else:
merged_dict[value].append(key)
for key in merged_dict:
if len(merged_dict[key]) == 1:
merged_dict[key] = merged_dict[key][0]
else:
merged_dict[key] = '-'.join([str(k)
for k in sorted(merged_dict[key])])
return merged_dict
test_dict1 = {1: 6, 8: 1, 9: 3, 10: 3, 12: 6, 4: 9, 2: 3}
merged_dict1 = merge_keys(test_dict1)
print(merged_dict1)
test_dict2 = {1: 6, 8: 1, 9: 3, 4: 9, 2: 3}
merged_dict2 = merge_keys(test_dict2)
print(merged_dict2)
|
Output
{6: '1-12', 1: 8, 3: '2-9-10', 9: 4}
{6: 1, 1: 8, 3: '2-9', 9: 4}
Time complexity: O(N log(N)) due to sorting the merged keys
Auxiliary Space: O(N)
Method – Using itertools.groupby()
Steps:
- Initialize an empty dictionary res.
- Use itertools.groupby() to group the original dictionary’s items by their values, and sort them based on the values.
- Loop over the groups, and for each group, get the keys and values and merge the keys using ‘-‘.join() if there is more than one key, otherwise just use the single key.
- Assign the merged key and value to the res dictionary and print the res dictionary.
Below is the implementation of the above approach:
Python3
import itertools
from functools import reduce
test_dict = {1: 6, 8: 1, 9: 3, 10: 3, 12: 6, 4: 9, 2: 3}
print("The original dictionary is : " + str(test_dict))
res = {}
for val, grp in itertools.groupby(sorted(test_dict.items(), key=lambda x: x[1]), lambda x: x[1]):
keys = [str(i[0]) for i in list(grp)]
if len(keys) == 1:
res[keys[0]] = val
else:
res['-'.join(keys)] = val
print("The required result : " + str(res))
|
Output
The original dictionary is : {1: 6, 8: 1, 9: 3, 10: 3, 12: 6, 4: 9, 2: 3}
The required result : {'8': 1, '9-10-2': 3, '1-12': 6, '4': 9}
Time Complexity: O(n log n) (sorting the dictionary items)
Space Complexity: O(n) (creating the res dictionary and the keys list for each group)
Method – Using list comprehension
Steps:
- Create an empty dictionary res to store the result
- Using a set, extract all unique values from the given dictionary
- Using a dictionary comprehension, group the keys of the given dictionary according to their values in a dictionary temp
- Iterate over each key in temp and concatenate its values separated by ‘-‘ to create a new key in res, with the corresponding value being the original key value from temp
- Return res as the required result.
Python3
test_dict = {1: 6, 8: 1, 9: 3, 10: 3, 12: 6, 4: 9, 2: 3}
print("The original dictionary is : " + str(test_dict))
temp = {val: [key for key, value in test_dict.items() if value == val]
for val in set(test_dict.values())}
res = {}
for key in temp:
res['-'.join([str(ele) for ele in temp[key]])] = key
print("The required result : " + str(res))
|
Output
The original dictionary is : {1: 6, 8: 1, 9: 3, 10: 3, 12: 6, 4: 9, 2: 3}
The required result : {'8': 1, '9-10-2': 3, '1-12': 6, '4': 9}
Time Complexity: O(n^2), where n is the length of the input dictionary. This is because the dictionary comprehension used to group the keys by values iterates over the entire input dictionary for each unique value, resulting in n^2 operations.
Auxiliary Space: O(n), where n is the length of the input dictionary. This is because we create a dictionary temp to store the keys grouped by values, which can have a maximum of n key-value pairs. The dictionary res and the set of unique values also contribute to the space complexity, but they have a maximum size of n as well. Therefore, the overall space complexity is O(n).
Method 4: Using nested for loop
Approach:
- Initialize an empty dictionary merged_dict.
- Loop through each key-value pair in the original dictionary test_dict.
- Check if the value of the current key is already in the merged_dict as a key.
- If the value is not in merged_dict, add a new key-value pair with the value as key and a list containing the key as the value.
- If the value is already in merged_dict, append the key to the existing list of keys for that value.
- Convert the list of keys for each value into a string with ‘-‘ as the separator.
- Add the new key-value pair to the res dictionary with the string of merged keys as the key and the value as the value.
- Print the resultant list.
Python3
test_dict = {1: 6, 8: 1, 9: 3, 10: 3, 12: 6, 4: 9, 2: 3}
print("The original dictionary is : " + str(test_dict))
merged_dict = {}
res = {}
for key, value in test_dict.items():
if value in merged_dict:
merged_dict[value].append(key)
else:
merged_dict[value] = [key]
for value in merged_dict:
key_str = '-'.join([str(key) for key in merged_dict[value]])
res[key_str] = value
print("The required result : " + str(res))
|
Output
The original dictionary is : {1: 6, 8: 1, 9: 3, 10: 3, 12: 6, 4: 9, 2: 3}
The required result : {'1-12': 6, '8': 1, '9-10-2': 3, '4': 9}
Time complexity: O(n), where n is the number of key-value pairs in the dictionary.
Auxiliary space: O(n), to store the merged_dict and res dictionaries.
Similar Reads
Python | Merge Python key values to list
Sometimes, while working with Python, we might have a problem in which we need to get the values of dictionary from several dictionaries to be encapsulated into one dictionary. This type of problem can be common in domains in which we work with relational data like in web developments. Let's discuss
4 min read
Python - Merge List value Keys to Matrix
Sometimes, while working with Python dictionary, we can have a problem in which we need to perform the merger of certain keys in dictionary. In this, we tend to form a matrix of resultant singular key. This kind of problem can have applications in data domains. Let's discuss certain way in which thi
4 min read
Merge Key Value Lists into Dictionary Python
Sometimes, while working with lists, we can come forward with a problem in which we need to perform the merge function in which we have the key list and need to create dictionary mapping keys with corresponding value in other list. Let's discuss certain ways in which this task can be performed. Merg
8 min read
Python | List value merge in dictionary
Sometimes, while working with dictionaries, we can have a problem in which we have many dictionaries and we are required to merge like keys. This problem seems common, but complex is if the values of keys are list and we need to add elements to list of like keys. Let's discuss way in which this prob
5 min read
Python - Group keys to values list
Sometimes, while working with Python dictionaries, we can have problem in which we need to find all possible values of all keys in a dictionary. This utility is quite common and can occur in many domains including day-day programming and school programming. Lets discuss certain way in which this tas
5 min read
Python - Mapping Key Values to Dictionary
We are given two list and we need to map key to values of another list so that it becomes dictionary. For example, we are given two list k = ['a', 'b', 'c'] and v = [1, 2, 3] we need to map the keys of list k to the values of list v so that the resultant output should be {'a': 1, 'b': 2, 'c': 3}. Us
3 min read
Python Print Dictionary Keys and Values
When working with dictionaries, it's essential to be able to print their keys and values for better understanding and debugging. In this article, we'll explore different methods to Print Dictionary Keys and Values. Example: Using print() Method [GFGTABS] Python my_dict = {'a': 1, 'b'
2 min read
Get specific keys' values - Python
Our task is to retrieve values associated with specific keys from a dictionary. This is especially useful when we only need to access certain pieces of data rather than the entire dictionary. For example, suppose we have the following dictionary: d = {'name': 'John', 'age': 25, 'location': 'New York
3 min read
Minimum Value Keys in Dictionary - Python
We are given a dictionary and need to find all the keys that have the minimum value among all key-value pairs. The goal is to identify the smallest value in the dictionary and then collect every key that matches it. For example, in {'a': 3, 'b': 1, 'c': 2, 'd': 1}, the minimum value is 1, so the res
4 min read
Python Merge Dictionaries with Same Keys
When working with dictionaries in Python, you should understand that they are mutable, unordered collections of key-value pairs. This flexibility allows us to quickly merge dictionaries, but what happens when two dictionaries have the same key? Python allows us to manage this situation. In this arti
3 min read