RustedSciThe 0.4.8

#![allow(dead_code)]

use std::env;

pub(crate) fn env_usize(name: &str, default: usize) -> usize {
    env::var(name)
        .ok()
        .and_then(|value| value.parse::<usize>().ok())
        .filter(|value| *value > 0)
        .unwrap_or(default)
}

pub(crate) fn mean(values: &[f64]) -> f64 {
    if values.is_empty() {
        return f64::NAN;
    }
    values.iter().copied().sum::<f64>() / values.len() as f64
}

pub(crate) fn stddev(values: &[f64], mean: f64) -> f64 {
    if values.len() <= 1 {
        return 0.0;
    }
    let variance = values
        .iter()
        .map(|value| {
            let delta = *value - mean;
            delta * delta
        })
        .sum::<f64>()
        / values.len() as f64;
    variance.sqrt()
}