# Mapped list average

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']) # 5.0