groupby

Функция groupby

itertools.groupby(iterable, key=None)

Пример использования:

from pprint import pprint
from dataclasses import dataclass
import operator

@dataclass(frozen=True)
class Book:
    title: str
    author: str


In [75]: books
Out[75]:
[Book(title='1984', author='George Orwell'),
 Book(title='The Martian Chronicles', author='Ray Bradbury'),
 Book(title='The Hobbit', author='J.R.R. Tolkien'),
 Book(title='Animal Farm', author='George Orwell'),
 Book(title='Fahrenheit 451', author='Ray Bradbury'),
 Book(title='The Lord of the Rings (1-3)', author='J.R.R. Tolkien'),
 Book(title='Harry Potter and the Sorcerer’s Stone', author='J.K. Rowling'),
 Book(title='To Kill a Mockingbird', author='Harper Lee')]


In [76]: list(groupby(books, operator.attrgetter('author')))
Out[76]:
[('George Orwell', <itertools._grouper at 0xb473f3ec>),
 ('Ray Bradbury', <itertools._grouper at 0xb473f12c>),
 ('J.R.R. Tolkien', <itertools._grouper at 0xb473f98c>),
 ('George Orwell', <itertools._grouper at 0xb473f7cc>),
 ('Ray Bradbury', <itertools._grouper at 0xb473f40c>),
 ('J.R.R. Tolkien', <itertools._grouper at 0xb473f74c>),
 ('J.K. Rowling', <itertools._grouper at 0xb473ffcc>),
 ('Harper Lee', <itertools._grouper at 0xb473fbec>)]


In [81]: for key, item in groupby(books, operator.attrgetter('author')):
    ...:     print(key.ljust(20), list(item))
    ...:
George Orwell        [Book(title='1984', author='George Orwell')]
Ray Bradbury         [Book(title='The Martian Chronicles', author='Ray Bradbury')]
J.R.R. Tolkien       [Book(title='The Hobbit', author='J.R.R. Tolkien')]
George Orwell        [Book(title='Animal Farm', author='George Orwell')]
Ray Bradbury         [Book(title='Fahrenheit 451', author='Ray Bradbury')]
J.R.R. Tolkien       [Book(title='The Lord of the Rings (1-3)', author='J.R.R. Tolkien')]
J.K. Rowling         [Book(title='Harry Potter and the Sorcerer’s Stone', author='J.K. Rowling')]
Harper Lee           [Book(title='To Kill a Mockingbird', author='Harper Lee')]


In [83]: sorted_books = sorted(books, key=operator.attrgetter('author'))

In [84]: sorted_books
Out[84]:
[Book(title='1984', author='George Orwell'),
 Book(title='Animal Farm', author='George Orwell'),
 Book(title='To Kill a Mockingbird', author='Harper Lee'),
 Book(title='Harry Potter and the Sorcerer’s Stone', author='J.K. Rowling'),
 Book(title='The Hobbit', author='J.R.R. Tolkien'),
 Book(title='The Lord of the Rings (1-3)', author='J.R.R. Tolkien'),
 Book(title='The Martian Chronicles', author='Ray Bradbury'),
 Book(title='Fahrenheit 451', author='Ray Bradbury')]

In [85]: for key, item in groupby(sorted_books, operator.attrgetter('author')):
    ...:     print(key.ljust(20), list(item))
    ...:
George Orwell        [Book(title='1984', author='George Orwell'), Book(title='Animal Farm', author='George Orwell')]
Harper Lee           [Book(title='To Kill a Mockingbird', author='Harper Lee')]
J.K. Rowling         [Book(title='Harry Potter and the Sorcerer’s Stone', author='J.K. Rowling')]
J.R.R. Tolkien       [Book(title='The Hobbit', author='J.R.R. Tolkien'), Book(title='The Lord of the Rings (1-3)', author='J.R.R. Tolkien')]
Ray Bradbury         [Book(title='The Martian Chronicles', author='Ray Bradbury'), Book(title='Fahrenheit 451', author='Ray Bradbury')]

In [86]: books_by_author = {}

In [87]: for key, item in groupby(sorted_books, operator.attrgetter('author')):
    ...:     books_by_author[key] = list(item)
    ...:

In [90]: pprint(books_by_author)
{'George Orwell': [Book(title='1984', author='George Orwell'),
                   Book(title='Animal Farm', author='George Orwell')],
 'Harper Lee': [Book(title='To Kill a Mockingbird', author='Harper Lee')],
 'J.K. Rowling': [Book(title='Harry Potter and the Sorcerer’s Stone', author='J.K. Rowling')],
 'J.R.R. Tolkien': [Book(title='The Hobbit', author='J.R.R. Tolkien'),
                    Book(title='The Lord of the Rings (1-3)', author='J.R.R. Tolkien')],
 'Ray Bradbury': [Book(title='The Martian Chronicles', author='Ray Bradbury'),
                  Book(title='Fahrenheit 451', author='Ray Bradbury')]}