17 lines
471 B
Python
17 lines
471 B
Python
from collections import defaultdict
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from typing import Callable, Collection, Dict, List, TypeVar
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__all__ = ["group_by"]
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K = TypeVar("K")
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T = TypeVar("T")
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def group_by(items: Collection[T], key_fn: Callable[[T], K]) -> Dict[K, List[T]]:
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"""Group an unsorted collection of items by a key derived via a function."""
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result: Dict[K, List[T]] = defaultdict(list)
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for item in items:
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key = key_fn(item)
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result[key].append(item)
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return result
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