21.1.4.2. 计算标准偏差
本实例计算一组测量值的标准偏差和 z 分数(z-score)。
标准偏差定义为方差的平方根(用 f32 浮点型的 [sqrt
] 计算),其中方差是每个测量值与平均数
之间的平方差的和
除以测量次数。
z 分数(z-score)是指单个测量值偏离数据集平均数
的标准差数。
fn mean(data: &[i32]) -> Option<f32> { let sum = data.iter().sum::<i32>() as f32; let count = data.len(); match count { positive if positive > 0 => Some(sum / count as f32), _ => None, } } fn std_deviation(data: &[i32]) -> Option<f32> { match (mean(data), data.len()) { (Some(data_mean), count) if count > 0 => { let variance = data.iter().map(|value| { let diff = data_mean - (*value as f32); diff * diff }).sum::<f32>() / count as f32; Some(variance.sqrt()) }, _ => None } } fn main() { let data = [3, 1, 6, 1, 5, 8, 1, 8, 10, 11]; let data_mean = mean(&data); println!("Mean is {:?}", data_mean); let data_std_deviation = std_deviation(&data); println!("Standard deviation is {:?}", data_std_deviation); let zscore = match (data_mean, data_std_deviation) { (Some(mean), Some(std_deviation)) => { let diff = data[4] as f32 - mean; Some(diff / std_deviation) }, _ => None }; println!("Z-score of data at index 4 (with value {}) is {:?}", data[4], zscore); }