27 lines
656 B
Markdown
27 lines
656 B
Markdown
---
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title: group_by
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tags: list,dictionary,intermediate
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---
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Groups the elements of a list based on the given function.
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- Use `defaultdict()` to initialize a dictionary.
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- Use `fn` in combination with a `for` loop and `dict.append()` to populate the dictionary.
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- Use the `dict()` constructor to convert it to a regular dictionary.
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```py
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from collections import defaultdict
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def group_by(lst, fn):
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d = defaultdict(list)
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for el in lst:
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d[fn(el)].append(el)
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return dict(d)
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```
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```py
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from math import floor
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group_by([6.1, 4.2, 6.3], floor) # {4: [4.2], 6: [6.1, 6.3]}
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group_by(['one', 'two', 'three'], len) # {3: ['one', 'two'], 5: ['three']}
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```
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