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 this task can be performed.

Input : test_dict = {‘Maths’: [1, 2], ‘gfg’: [4, 5], ‘CS’: [6]} 
Output : {‘merge_key’: [[4, 5], [6], [1, 2]]} 

Input : test_dict = {‘Maths’: [1], ‘gfg’: [4], ‘CS’: [9]} 
Output : {‘merge_key’: [[4], [9], [1]]}

Method 1: Using loop + pop() This task can be performed using brute force manner. In this, we iterate the keys and remove the keys using pop, reinitialize them after merging into a matrix. 

Python3

# Python3 code to demonstrate working of
# Merge List value Keys to Matrix
# Using loop + pop()

# initializing dictionary
test_dict = {'gfg' : [4, 5, 6],
             'is' : [8, 8, 9],
             'CS' : [1, 3, 8],
             'Maths' : [1, 2]}

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

# initializing list
que_list = ['gfg', 'CS', 'Maths']

# Merge List value Keys to Matrix
# Using loop + pop()
new_data = [test_dict.pop(ele) for ele in que_list]
test_dict["merge_key"] = new_data

# printing result
print("The dictionary after merging : " + str(test_dict))

Output : 

The original dictionary : {‘is’: [8, 8, 9], ‘gfg’: [4, 5, 6], ‘Maths’: [1, 2], ‘CS’: [1, 3, 8]} The dictionary after merging : {‘is’: [8, 8, 9], ‘merge_key’: [[4, 5, 6], [1, 3, 8], [1, 2]]}

Method 2: Using for loops

Approach

1. Initiate a for loop to access dictionary keys
2. If key is present in que_list append value of key to a list x
3. If not present assign that key and value to new dictionary res
4. After end of for loop assign key “merge_key” with value list x
5. Display res

Python3

# Python3 code to demonstrate working of
# Merge List value Keys to Matrix

# initializing dictionary
test_dict = {'gfg' : [4, 5, 6],
            'is' : [8, 8, 9],
            'CS' : [1, 3, 8],
            'Maths' : [1, 2]}

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

# initializing list
que_list = ['gfg', 'CS', 'Maths']

# Merge List value Keys to Matrix
x=[]
res=dict()
for i in list(test_dict.keys()):
    if i in que_list:
        x.append(test_dict[i])
    else:
        res[i]=test_dict[i]
res["merge_key"]=x

# printing result
print("The dictionary after merging : " + str(res))

Output

The original dictionary : {'gfg': [4, 5, 6], 'is': [8, 8, 9], 'CS': [1, 3, 8], 'Maths': [1, 2]}
The dictionary after merging : {'is': [8, 8, 9], 'merge_key': [[4, 5, 6], [1, 3, 8], [1, 2]]}

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

Method 3: Using dictionary comprehension

This approach uses a dictionary comprehension to create a new dictionary new_data that only includes the keys from que_list. Then, it converts the values of this new dictionary to a list and adds it to the original dictionary under the key “merge_key”. This approach should have the same time complexity as the previous methods, but it may require more auxiliary space due to the creation of the new dictionary.

Python3

# Python3 code to demonstrate working of
# Merge List value Keys to Matrix
# Using dictionary comprehension

# initializing dictionary
test_dict = {'gfg' : [4, 5, 6],
             'is' : [8, 8, 9],
             'CS' : [1, 3, 8],
             'Maths' : [1, 2]}

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

# initializing list
que_list = ['gfg', 'CS', 'Maths']

# Merge List value Keys to Matrix
# Using dictionary comprehension
new_data = {key: test_dict[key] for key in que_list}
test_dict["merge_key"] = list(new_data.values())

# printing result
print("The dictionary after merging : " + str(test_dict))

Output

The original dictionary : {'gfg': [4, 5, 6], 'is': [8, 8, 9], 'CS': [1, 3, 8], 'Maths': [1, 2]}
The dictionary after merging : {'gfg': [4, 5, 6], 'is': [8, 8, 9], 'CS': [1, 3, 8], 'Maths': [1, 2], 'merge_key': [[4, 5, 6], [1, 3, 8], [1, 2]]}

Time complexity: O(n), where n is the number of elements in the dictionary, 
Auxiliary space: O(n).