21 lines
534 B
Markdown
21 lines
534 B
Markdown
---
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title: group_by
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tags: list,object,beginner
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---
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Groups the elements of a list based on the given function.
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Use `map()` and `fn` to map the values of the list to the keys of an object.
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Use list comprehension to map each element to the appropriate `key`.
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```py
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def group_by(lst, fn):
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return {key : [el for el in lst if fn(el) == key] for key in map(fn,lst)}
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```
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```py
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import math
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group_by([6.1, 4.2, 6.3], math.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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