pub fn get_cv(values: &[f64]) -> f64 {
let (variance, mean) = get_variance_mean(values);
let sdev = variance.sqrt();
sdev / mean
}
pub fn get_mean(values: &[f64]) -> f64 {
let sum: f64 = values.iter().sum();
sum / values.len() as f64
}
fn get_variance_mean(values: &[f64]) -> (f64, f64) {
let mean = get_mean(values);
let (first, second) = values.iter().fold((0., 0.), |acc, v| {
let dev = v - mean;
(acc.0 + dev * dev, acc.1 + dev)
});
((first - (second * second / values.len() as f64)) / (values.len() as f64 - 1.), mean)
}