Function mean_by 

pub fn mean_by<T, F>(collection: &[T], iteratee: F) -> f64
where
    F: Fn(&T) -> f64,

Calculates the mean value of a collection after applying a transformation function to each element.

Arguments

• collection - A slice of items to calculate the mean from
• iteratee - A function that transforms each item before calculating the mean

Returns

The mean value after applying the transformation

Examples

use lowdash::mean_by;

let objects = vec![(1, 4), (2, 6), (3, 8)];
let mean = mean_by(&objects, |&(x, _)| x as f64);
assert!((mean - 2.0).abs() < f64::EPSILON);

// Calculate mean of y coordinates
let mean_y = mean_by(&objects, |&(_, y)| y as f64);
assert!((mean_y - 6.0).abs() < f64::EPSILON);