averageBy<T extends num> method Null safety

double averageBy<T extends num>(
  1. T selector(
    1. int index,
    2. E
    )
)

Returns an average of all values produced by selector function or double.nan if there are no elements.

For example:

[jon, amy, joe].averageBy((_, student) => student.age) // => average age

Implementation

double averageBy<T extends num>(T Function(int index, E) selector) =>
    mapIndexed(selector).average();