1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92
//! # Euclidian Metric Distance
//!
//! The Euclidean distance (L2) between two points \\( x \\) and \\( y \\) in n-space is defined as
//!
//! \\[ d(x, y) = \sqrt{\sum_{i=1}^n (x-y)^2} \\]
//!
//! Example:
//!
//! ```
//! use smartcore::metrics::distance::Distance;
//! use smartcore::metrics::distance::euclidian::Euclidian;
//!
//! let x = vec![1., 1.];
//! let y = vec![2., 2.];
//!
//! let l2: f64 = Euclidian::new().distance(&x, &y);
//! ```
//!
//! <script src="https://polyfill.io/v3/polyfill.min.js?features=es6"></script>
//! <script id="MathJax-script" async src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script>
#[cfg(feature = "serde")]
use serde::{Deserialize, Serialize};
use std::marker::PhantomData;
use crate::linalg::basic::arrays::ArrayView1;
use crate::numbers::basenum::Number;
use super::Distance;
/// Euclidean distance is a measure of the true straight line distance between two points in Euclidean n-space.
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
#[derive(Debug, Clone)]
pub struct Euclidian<T> {
_t: PhantomData<T>,
}
impl<T: Number> Default for Euclidian<T> {
fn default() -> Self {
Self::new()
}
}
impl<T: Number> Euclidian<T> {
/// instatiate the initial structure
pub fn new() -> Euclidian<T> {
Euclidian { _t: PhantomData }
}
/// return sum of squared distances
#[inline]
pub(crate) fn squared_distance<A: ArrayView1<T>>(x: &A, y: &A) -> f64 {
if x.shape() != y.shape() {
panic!("Input vector sizes are different.");
}
let sum: f64 = x
.iterator(0)
.zip(y.iterator(0))
.map(|(&a, &b)| {
let r = a - b;
(r * r).to_f64().unwrap()
})
.sum();
sum
}
}
impl<T: Number, A: ArrayView1<T>> Distance<A> for Euclidian<T> {
fn distance(&self, x: &A, y: &A) -> f64 {
Euclidian::squared_distance(x, y).sqrt()
}
}
#[cfg(test)]
mod tests {
use super::*;
#[cfg_attr(
all(target_arch = "wasm32", not(target_os = "wasi")),
wasm_bindgen_test::wasm_bindgen_test
)]
#[test]
fn squared_distance() {
let a = vec![1, 2, 3];
let b = vec![4, 5, 6];
let l2: f64 = Euclidian::new().distance(&a, &b);
assert!((l2 - 5.19615242).abs() < 1e-8);
}
}