How to Group List Elements by Key in Python

In Python, you can group elements of a list by a key using the itertools.groupby() function. Here’s a simple explanation and example:

Steps:

1. Sort the List: groupby() works on sorted data. Make sure your list is sorted by the key you want to group by.
2. Use groupby(): Pass the sorted list and a key function to groupby(). The key function specifies the attribute or property to group by.

   from itertools import groupby
   
   # List of dictionaries
   data = [
       {'name': 'Alice', 'age': 25},
       {'name': 'Bob', 'age': 30},
       {'name': 'Alice', 'age': 28},
       {'name': 'Charlie', 'age': 25}
   ]
   
   # Sort the list by 'name'
   data.sort(key=lambda x: x['name'])
   
   # Group by 'name'
   grouped = groupby(data, key=lambda x: x['name'])
   
   # Display groups
   for key, group in grouped:
       print(f"{key}: {[item for item in group]}")
   

Output:

Alice: [{'name': 'Alice', 'age': 25}, {'name': 'Alice', 'age': 28}]
Bob: [{'name': 'Bob', 'age': 30}]
Charlie: [{'name': 'Charlie', 'age': 25}]