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# Mapped list average

Python, Math, List · Nov 2, 2020

Calculates the average of a list, after mapping each element to a value using the provided function.

- Use
`map()`

to map each element to the value returned by `fn`

.
- Use
`sum()`

to sum all of the mapped values, divide by `len(lst)`

.
- Omit the last argument,
`fn`

, to use the default identity function.

def average_by(lst, fn = lambda x: x):
return sum(map(fn, lst), 0.0) / len(lst)
average_by([{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }], lambda x: x['n'])

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