Convert Tuples to Dictionary - Python

The task is to convert a list of tuples into a dictionary where each tuple contains two element . The first element of each tuple becomes the key and the second element becomes the value. If a key appears multiple times its values should be grouped together, typically in a list.

For example, given the list li = [("akash", 10), ("gaurav", 12), ("anand", 14), ("akash", 20)], the goal is to convert it into a dictionary where each key maps to a list of its corresponding values, like {'akash': [10, 20], 'gaurav': [12], 'anand': [14]}.

Using groupby()

We can use groupby() to convert tuples into a dictionary where the first element of each tuple becomes the key, and the second element becomes the value. However before using groupby() the list must be sorted by the key, as groupby() only groups consecutive elements with the same value.

from itertools import groupby

li = [("akash", 10), ("gaurav", 12), ("anand", 14), 
      ("suraj", 20), ("akhil", 25), ("ashish", 30)]

# Sort the list before applying groupby
li.sort(key=lambda x: x[0])
res = {key: [value for key, value in group] for key, group in groupby(li, key=lambda x: x[0])}
print(res)

{'akash': [10], 'akhil': [25], 'anand': [14], 'ashish': [30], 'gaurav': [12], 'suraj': [20]}

Explanation:

• li.sort(): This sorts the list li based on the first element of each tuple.
• groupby(li, key=lambda x: x[0]): This groups consecutive elements by the first element of each tuple.

Using defaultdict()

defaultdict() from the collections module simplifies this process of conversion by automatically initializing default values for missing keys. This is especially useful for grouping values under a key without needing manual checks for key existence.

from collections import defaultdict

li = [("akash", 10), ("gaurav", 12), ("anand", 14), 
      ("suraj", 20), ("akhil", 25), ("ashish", 30)]

d = defaultdict(list)
for a, b in li:
    d[a].append(b)

print(dict(d))

{'akash': [10], 'gaurav': [12], 'anand': [14], 'suraj': [20], 'akhil': [25], 'ashish': [30]}

Explanation:

• defaultdict(list):This creates a dictionary where each key automatically has an empty list as its default value.
• for a, b in li: This iterates through the list of tuples li, where a is the key and b is the value.
• d[a].append(b):This appends the value b to the list corresponding to the key a.
• dict(d):This converts the defaultdict to dictionary d .

Using dict.get()

dict.get() method that checks if a key exists in the dictionary. If it doesn't, it returns a default value . The advantage is that it eliminates the need for explicit checks like if a not in dictionery.

li = [("akash", 10), ("gaurav", 12), ("anand", 14), 
      ("suraj", 20), ("akhil", 25), ("ashish", 30)]
d = {}

for a, b in li:
    d[a] = d.get(a, []) + [b]

print(d)

{'akash': [10], 'gaurav': [12], 'anand': [14], 'suraj': [20], 'akhil': [25], 'ashish': [30]}

Explanation:

• for a, b in li: This loop iterates through the list li, where a is the key and b is the value.
• d.get(a, []): This checks whether the key a exists in the dictionary d. If it does not exist, it returns an empty list as the default value.
• d[a] = d.get(a, []) + [b]: This concatenates the value b to the existing list for the key a and initializes a new list if the key is not already present.

Using loop

This method involves iterating through the list and manually checking if the key already exists in the dictionary. If the key doesn’t exist, it initializes the key with an empty list. This method is efficient, but it requires more lines of code than defaultdict().

li = [("akash", 10), ("gaurav", 12), ("anand", 14), 
      ("suraj", 20), ("akhil", 25), ("ashish", 30)]
d = {}

for a, b in li:
    if a not in d:
        d[a] = []
    d[a].append(b)

print(d)

{'akash': [10], 'gaurav': [12], 'anand': [14], 'suraj': [20], 'akhil': [25], 'ashish': [30]}

Explanation:

• for a, b in li: This loop iterates through the list li, where a is the key and b is the value.
• if a not in d: This checks whether the key a is already in the dictionary d.
• d[a] = []: If the key is not present, it initializes an empty list for that key.
• d[a].append(b): It appends the value b to the list corresponding to the key a.