Group items by a key
Collect a list of records into a dictionary of lists keyed by a field or function result.
- Python
- GreenSnippets
- MIT
- Executed with Python 3.11
from collections import defaultdict
def group_by(items, key):
groups = defaultdict(list)
for item in items:
groups[key(item)].append(item)
return dict(groups)Example / expected output
group_by(["apple", "avocado", "banana"], key=lambda s: s[0])
# {'a': ['apple', 'avocado'], 'b': ['banana']}How it works
defaultdict(list) removes the need to check whether a key exists. The key can be any callable, so the same helper groups by field, by first letter, by computed bucket and so on. Order within each group is the input order.
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