24 lines
647 B
Markdown
24 lines
647 B
Markdown
---
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title: Mapped list average
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tags: math,list
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expertise: intermediate
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firstSeen: 2019-08-20T11:55:10+03:00
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lastUpdated: 2020-11-02T19:27:07+02:00
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---
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Calculates the average of a list, after mapping each element to a value using the provided function.
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- Use `map()` to map each element to the value returned by `fn`.
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- Use `sum()` to sum all of the mapped values, divide by `len(lst)`.
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- Omit the last argument, `fn`, to use the default identity function.
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```py
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def average_by(lst, fn = lambda x: x):
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return sum(map(fn, lst), 0.0) / len(lst)
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```
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```py
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average_by([{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }], lambda x: x['n'])
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# 5.0
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```
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