added Jaccard distance

Author: skywardfire1

src/metrics/distance/jaccard.rs

@@ -0,0 +1,101 @@
+//! # Jaccard Distance
+//!
+//! Jaccard Distance measures dissimilarity between two integer-valued vectors of the same length.
+//! Given two vectors \\( x \in ℝ^n \\), \\( y \in ℝ^n \\) the Jaccard distance between \\( x \\) and \\( y \\) is defined as
+//!
+//! \\[ d(x, y) = 1 - \frac{|x \cap y|}{|x \cup y|} \\]
+//!
+//! where \\(|x \cap y|\\) is the number of positions where both vectors are non-zero,
+//! and \\(|x \cup y|\\) is the number of positions where at least one of the vectors is non-zero.
+//!
+//! Example:
+//!
+//! ```
+//! use smartcore::metrics::distance::Distance;
+//! use smartcore::metrics::distance::jaccard::Jaccard;
+//!
+//! let a = vec![1, 0, 1, 1];
+//! let b = vec![1, 1, 0, 1];
+//!
+//! let j: f64 = Jaccard::new().distance(&a, &b);
+//!
+//! ```
+//!
+//! <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 super::Distance;
+use crate::linalg::basic::arrays::ArrayView1;
+use crate::numbers::basenum::Number;
+
+/// Jaccard distance between two integer-valued vectors
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+#[derive(Debug, Clone)]
+pub struct Jaccard<T: Number> {
+    _t: PhantomData<T>,
+}
+
+impl<T: Number> Jaccard<T> {
+    /// instatiate the initial structure
+    pub fn new() -> Jaccard<T> {
+        Jaccard { _t: PhantomData }
+    }
+}
+
+impl<T: Number> Default for Jaccard<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<T: Number, A: ArrayView1<T>> Distance<A> for Jaccard<T> {
+    fn distance(&self, x: &A, y: &A) -> f64 {
+        if x.shape() != y.shape() {
+            panic!("Input vector sizes are different");
+        }
+
+        let (intersection, union): (usize, usize) = x
+            .iterator(0)
+            .zip(y.iterator(0))
+            .map(|(a, b)| {
+                let a_nz = *a != T::zero();
+                let b_nz = *b != T::zero();
+
+                match (a_nz, b_nz) {
+                    (true, true) => (1, 1),
+                    (true, false) | (false, true) => (0, 1),
+                    (false, false) => (0, 0),
+                }
+            })
+            .fold((0, 0), |acc, v| (acc.0 + v.0, acc.1 + v.1));
+
+        if union == 0 {
+            0.0
+        } else {
+            1.0 - intersection as f64 / union as f64
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[cfg_attr(
+        all(target_arch = "wasm32", not(target_os = "wasi")),
+        wasm_bindgen_test::wasm_bindgen_test
+    )]
+    #[test]
+    fn jaccard_distance() {
+        let a = vec![1, 0, 1, 1];
+        let b = vec![1, 1, 0, 1];
+
+        let j: f64 = Jaccard::new().distance(&a, &b);
+
+        assert!((j - 0.5).abs() < 1e-8);
+    }
+}

src/metrics/distance/mod.rs

@@ -19,6 +19,8 @@ pub mod cosine;
 pub mod euclidian;
 /// Hamming Distance between two strings is the number of positions at which the corresponding symbols are different.
 pub mod hamming;
+/// Jaccard distance between two integer-valued vectors.
+pub mod jaccard;
 /// The Mahalanobis distance is the distance between two points in multivariate space.
 pub mod mahalanobis;
 /// Also known as rectilinear distance, city block distance, taxicab metric.
@@ -67,6 +69,11 @@ impl Distances {
         hamming::Hamming::new()
     }
 
+    /// Jaccard distance, see [`Jaccard`](jaccard/index.html)
+    pub fn jaccard<T: Number>() -> jaccard::Jaccard<T> {
+        jaccard::Jaccard::new()
+    }
+
     /// Mahalanobis distance, see [`Mahalanobis`](mahalanobis/index.html)
     pub fn mahalanobis<T: Number, M: Array2<T>, C: Array2<f64> + LUDecomposable<f64>>(
         data: &M,