Python – Append Similar Values as Key

Sometimes, while working with data, we can have problems in which we need to categorize a particular list and values to similar keys. This can be problem in counting data. Like counting votes or counting coins. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using loop
This is brute way in which this task can be performed. In this, we run a loop to add values to dictionary value list, if not present we dynamically create key and perform append.

# Python3 code to demonstrate working of
# Append Similar Values as Key
# Using loop

# initializing list
test_list = ['Manjeet', 'Nikhil', 'Akshat', 'Akash',
            'Manjeet', 'Akash', 'Akshat', 'Manjeet']

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

# Append Similar Values as Key
# Using loop
res = dict()
for ele in test_list:
    try:
        res[ele].append(ele)
    except KeyError:
        res[ele] = [ele]

# printing result
print("The similar values dictionary is : " + str(res))

Output :

The original list is : [‘Manjeet’, ‘Nikhil’, ‘Akshat’, ‘Akash’, ‘Manjeet’, ‘Akash’, ‘Akshat’, ‘Manjeet’]
The similar values dictionary is : {‘Nikhil’: [‘Nikhil’], ‘Manjeet’: [‘Manjeet’, ‘Manjeet’, ‘Manjeet’], ‘Akash’: [‘Akash’, ‘Akash’], ‘Akshat’: [‘Akshat’, ‘Akshat’]}

Method #2 : Using defaultdict() + loop
The combination of above functions can be used to solve this problem. In this, we pre initialize the dictionary using defaultdict().

# Python3 code to demonstrate working of
# Append Similar Values as Key
# Using defaultdict() + loop
from collections import defaultdict

# initializing list
test_list = ['Manjeet', 'Nikhil', 'Akshat', 'Akash',
         'Manjeet', 'Akash', 'Akshat', 'Manjeet']

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

# Append Similar Values as Key
# Using defaultdict() + loop
res = defaultdict(list)
for sub in test_list:
    res[sub].append(sub)

# printing result
print("The similar values dictionary is : " + str(dict(res)))

Output :

The original list is : [‘Manjeet’, ‘Nikhil’, ‘Akshat’, ‘Akash’, ‘Manjeet’, ‘Akash’, ‘Akshat’, ‘Manjeet’]
The similar values dictionary is : {‘Nikhil’: [‘Nikhil’], ‘Manjeet’: [‘Manjeet’, ‘Manjeet’, ‘Manjeet’], ‘Akash’: [‘Akash’, ‘Akash’], ‘Akshat’: [‘Akshat’, ‘Akshat’]}